IIRC, he repented on his death bed. Perhaps someone can check into that.
With regards to the "deathbed confession":
There is some mystery about the death of Archbishop Lefebvre--have you heard whether he was reconciled with the Church?
There is, and I am trying to confirm this--there are two priests who are still members of the Pius X Society. And they have in turn told me, in secret--but I have been publicizing it--that when Father Schmidberger, the Superior General at the time walked into the room where he {Archbishop Lefebvre} was lying on his deathbed, Archbishop Lefebvre looked at him and said, 'What are you doing here?' And Father Schmidberger said, 'I am just here to say farewell--to wish you well and that I will be praying for you'. And Archbishop Lefebvre said to him, 'I didn't ask you to come, you can leave now--because of you, I'm in this mess.' I know that Father Schmidburger was very instrumental in forcing the Archbishop's hand, so to speak, to do the consecrations. I'm sure it was the spirit of the Archbishop to go along with the consecrations, but Father Schmidburger definitely was a leading role in pushing him to do the consecrations....
So, I really think there was repentance on the part of Archbishop Lefebvre before he died. One of those who told me this story witnessed this incident and he claims that's what took place. And that's my prayer, that he had that repentance before he died."
A conversation with Fr. John Rizzo That's the closest thing I could find to confirm (or deny) any deathbed confession on the part of Archbishop Lefebvre.
As for Lefebvre signing all 16 Vatican II documents, this seems to be undeniable fact, as even Bishop Fellay doesn't deny it. Source.
Actually that article seems to deserve a thread of its own, (if it doesn't have one already I may post it myself later), of particular relevance is this portion of the interview:
Q: Archbishop Lefebvre signed all 16 documents of the Second Vatican Council. After the Council, he was very critical of the documents and even sent a dubia to the Holy See requesting clarification on religious liberty. However, Archbishop Lefebvre never rejected all the documents of the Second Vatican Council in totality.
A: And we don't do so either. It is not a matter of rejecting or accepting.
The questions are, "Are these documents good? Are these documents nurturing the Faith? Are they good for the survival of the Church or not?"
And the more we go on, the more we see the ambiguities in the Council — which at a certain time seemed to be reconcilable to be correctly interpreted with Tradition, not including the very obvious errors — the further we go on, and the more we see that this is an impossible job.