I'm going to have to ponder this thread some more, but the one thing that immєdιαtely comes to mind is that this argument contradicts all the "hurr durr dogmas don't have to be interpreted" pseudo-Protestants on here.  Because Florence pretty clearly talks about the *fires* of Hell for all non Catholics.

So, for e.g. what precisely happened to the OT Just in limbo, so that they could go to Heaven? They clearly were already justified, and they were ultimately going to be saved. But did Our Lord Baptize them?

I agree that Our Lord must have changed something about them. Some say that, while they earlier had only implicit faith in Him, He brought them to explicit faith, and thus they were enabled to enter Heaven.

“Grant, therefore, to Thy servant the gift of Thy grace which he never rejected, who on the day before his death refused to restore the privileges of the temples although he was pressed by those whom he could well have feared. A crowd of pagans was present, the Senate entreated, but he was not afraid to displease men so long as he pleased Thee alone in Christ. He who had Thy Spirit, how has he not received Thy grace? Or, if the fact disturbs you that the mysteries have not been solemnly celebrated, then you should realize that not even martyrs are crowned if they are catechumens, for they are not crowned if they are not initiated. But if they are washed in their own blood, his piety also and his desire have washed him.” (De Consolatione in obitu Valentiniani, 51-54 = PL 16, 1374-75. Translated by Roy J. Deferrari, Ph.D., in Funeral Orations by St. Gregory nαzιanzen and St. Ambrose, pp. 287-288)
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The translation is not the problem here. The last two sentences, which seem contradictory, are exactly accurate from the Latin of Migne’s Patrologia Latina. In the next to the last sentence Saint Ambrose says “that not even martyrs are crowned if they are catechumens, for they are not crowned if they are not initiated.” Does he mean that they are saved, but not crowned? Then, in the last sentence, he says that “if they [martyrs] are washed in their own blood, his piety also and his desire have washed him.” I cannot understand what the holy doctor is affirming or denying in these sentences. Perhaps something is missing from the original transcription itself.

I was always taught that there were 2 reasons why the OT just could not enter heaven.  The first reason is sound - the OT just had to wait in Limbo until Christ opened the gates of heaven on Ascension Thursday.  Christ, being the Redeemer and Reconciler of man with God, was the only one, and the first one, to re-enter heaven.  Christ was a new-Adam, who conquered Original Sin.
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The second reason, which is speculative, is that the OT just had to be baptized.  Even St John the Baptist, who was part of the Old Law, said that Christ would Baptize with the Holy Ghost.  And another reason would be that Christ would provide them the Holy Eucharist, but this is also speculative.  Would God require all of the OT Just to enter the Church (the perfect, fulfilled Church of the New Law) before entering Heaven?  I don't see why not.  But I also can't say for sure.
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Even Our Lady, who was full of grace, who never sinned, still needed a Redeemer.  She still called Our Lord Her Savior.  But if She was free from sin (the most justified person ever), why did She still need to be baptized?  Because She still did not have the baptismal character fully.  The Old Law was imperfect; it was a precursor; it was incomplete.  Christ completed the Old Law and the Holy Ghost started the Church on Pentacost.  Thus, it stands to reason, that to get into heaven under the New Law, you had to be baptized, receive the Eucharist, and become a perfect member of God's new kingdom.

And he said to them: Go ye into the whole world, and preach the gospel to every creature.  He that believeth and is baptized, shall be saved: but he that believeth not shall be condemned.