What's your proof that 5:55 is ambiguous and the context doesn't give it a proper meaning in a way that proves the authority of Ali (a) and the successors (a) in general?
Simply translating it as you please is not a proof. You have to justify your translation through Quran.
I will propose and attempt to justify the following translation per (1) Quranic context (2) Hadiths (3) Logic:
"Your Authority is only God, the Messenger, and those who granted security, those who keep up prayers/connections (to God) and give charity (even) while they bow. And whoever gives authority to God, the Messenger and those who granted security than the party of God, these are they who are successful.".
Momin is mostly meant to be believer, but when God applies the title to himself, it has alternative meaning which most translations have it as granter of safety and security.
The Ulil-Amr (a) are to be referred in matters of safety and fear, and hence, grant security to the people if relied on.
(1)Proof by hadith
There is a hadith in Alkafi, that when asked about the verse "...don't take a waleejatan other then God and the believers", that believers here meant those who grant security.
The one place God gives himself the title Al-Momin, it's practically almost all agreed upon, with some exceptions, that it means one who grants peace, security, and safety.
It's rational to conclude in special cases like the waleejatan verse, and verse not to take Awliya (authorities) other then Momineen, and that Momineen see your deeds with the God of the universe and the Messenger, it refers to alternative meaning and special meaning, then believers, but better translated as "those who give security/safety" just as the verse about God is better translated like that when the title Momin applies to Himself.
(2) Context
The Quran talks about previous books to be judgment sources, but, also talks about the role of Anbiya who were safeguarding the revelation and would judge for the Jews and judge for the scholars. It emphasizes on ruling and judging by what God revealed, then goes to a dialogue not to take awliya from those given the book before us.
The reason by flow is obvious to me, that, despite being handed down revelation and despite their duty to teach it's truth to the people, they are to not to be relied on as to what the Torah and Gospels actually teach.
They are not authorities over people despite their claim of representing the divine revelations and teachings.
In fact, some of them are authorities over others, and they don't agree upon who is the authority, which is one way of negating the authority of Christian and Jewish scholars.
Then it talks about not turning on backs to believers and addresses them and threatens them to bring about a people who God loves and they love him.
Then in this flow says "Your only Wali is....", which means the religious authority you have, and it's about the same claimed by Christian and Jewish leaders not to be taken as authorities.....
As believers are being addressed in this topic, and they themselves are not all religious authorities, but rather like the dialogue of Rasool and Ulil-Amr, it's those who grant security and safety with respect to the next world and this world as well, who are to be relied upon as authority.
Then it further emphasizes after that those taken as authorities from the people of the book, are those who religion has become a play pastime for them, a game of thrones and conjecture of desires.
This is not something that can only happen in the past, but can happen in the future. This is why God emphasized on the Wilayah of God and his chosen.
Backing it up in the Surah, it also flows back to the day God perfect his favor, and his favor linked to the reminder of God raising Prophets and Kings in the children of Israel, and that linked to the covenant and him sending Messengers reminded later, which is linked to the Twelve Captains (the true Navigators who were Messengers) in the covenant of the Children of Israel.
The flow is obvious, just as there was just Twelve Captains and not more or less, and they were the way to set the ship to safety and bring humans to peace and safety in this world and the next, here it's saying you have no other Wali to get guidance to what the Quran truly revealed except God himself (Quran by Quran), his Messenger (Sunnah), and those who grant safety those who keep up the prayers and give charity (even) while bowing who is a group that Imam Ali (a) represented when he gave his ring.
["yomen man rakabaha" (it grants safety to those who board it)]
(3) Logic
By rational logic, we aren't forbidden to love or be friends with people of the book, as Quran is clear only that type friendship and love was forbidden to those who fought the believers and prosecuted them due to their religion. When the same chapter talks about marrying people of the book, it's not forbidding friendship with them.
So aside from context, the meaning as friend is absurd. The same with ally, we are allowed to have allies other then believers.
That and Angels (a) are included in guardians and friends, but are not included in this verse if it means believers even though they believe, they are the ones conveying from God to Mohammad (s) about the hidden reality and revelation, so it doesn't make sense to call Gabriel a believer.
This is another reason why the best translation is the one I just provided.
Simply translating it as you please is not a proof. You have to justify your translation through Quran.
I will propose and attempt to justify the following translation per (1) Quranic context (2) Hadiths (3) Logic:
"Your Authority is only God, the Messenger, and those who granted security, those who keep up prayers/connections (to God) and give charity (even) while they bow. And whoever gives authority to God, the Messenger and those who granted security than the party of God, these are they who are successful.".
Momin is mostly meant to be believer, but when God applies the title to himself, it has alternative meaning which most translations have it as granter of safety and security.
The Ulil-Amr (a) are to be referred in matters of safety and fear, and hence, grant security to the people if relied on.
(1)Proof by hadith
There is a hadith in Alkafi, that when asked about the verse "...don't take a waleejatan other then God and the believers", that believers here meant those who grant security.
The one place God gives himself the title Al-Momin, it's practically almost all agreed upon, with some exceptions, that it means one who grants peace, security, and safety.
It's rational to conclude in special cases like the waleejatan verse, and verse not to take Awliya (authorities) other then Momineen, and that Momineen see your deeds with the God of the universe and the Messenger, it refers to alternative meaning and special meaning, then believers, but better translated as "those who give security/safety" just as the verse about God is better translated like that when the title Momin applies to Himself.
(2) Context
The Quran talks about previous books to be judgment sources, but, also talks about the role of Anbiya who were safeguarding the revelation and would judge for the Jews and judge for the scholars. It emphasizes on ruling and judging by what God revealed, then goes to a dialogue not to take awliya from those given the book before us.
The reason by flow is obvious to me, that, despite being handed down revelation and despite their duty to teach it's truth to the people, they are to not to be relied on as to what the Torah and Gospels actually teach.
They are not authorities over people despite their claim of representing the divine revelations and teachings.
In fact, some of them are authorities over others, and they don't agree upon who is the authority, which is one way of negating the authority of Christian and Jewish scholars.
Then it talks about not turning on backs to believers and addresses them and threatens them to bring about a people who God loves and they love him.
Then in this flow says "Your only Wali is....", which means the religious authority you have, and it's about the same claimed by Christian and Jewish leaders not to be taken as authorities.....
As believers are being addressed in this topic, and they themselves are not all religious authorities, but rather like the dialogue of Rasool and Ulil-Amr, it's those who grant security and safety with respect to the next world and this world as well, who are to be relied upon as authority.
Then it further emphasizes after that those taken as authorities from the people of the book, are those who religion has become a play pastime for them, a game of thrones and conjecture of desires.
This is not something that can only happen in the past, but can happen in the future. This is why God emphasized on the Wilayah of God and his chosen.
Backing it up in the Surah, it also flows back to the day God perfect his favor, and his favor linked to the reminder of God raising Prophets and Kings in the children of Israel, and that linked to the covenant and him sending Messengers reminded later, which is linked to the Twelve Captains (the true Navigators who were Messengers) in the covenant of the Children of Israel.
The flow is obvious, just as there was just Twelve Captains and not more or less, and they were the way to set the ship to safety and bring humans to peace and safety in this world and the next, here it's saying you have no other Wali to get guidance to what the Quran truly revealed except God himself (Quran by Quran), his Messenger (Sunnah), and those who grant safety those who keep up the prayers and give charity (even) while bowing who is a group that Imam Ali (a) represented when he gave his ring.
["yomen man rakabaha" (it grants safety to those who board it)]
(3) Logic
By rational logic, we aren't forbidden to love or be friends with people of the book, as Quran is clear only that type friendship and love was forbidden to those who fought the believers and prosecuted them due to their religion. When the same chapter talks about marrying people of the book, it's not forbidding friendship with them.
So aside from context, the meaning as friend is absurd. The same with ally, we are allowed to have allies other then believers.
That and Angels (a) are included in guardians and friends, but are not included in this verse if it means believers even though they believe, they are the ones conveying from God to Mohammad (s) about the hidden reality and revelation, so it doesn't make sense to call Gabriel a believer.
This is another reason why the best translation is the one I just provided.