I'm right with you on the issue of infalibility, Roscoe. It is precisely because the V2 teachings do not carry with them the mark of infalibility that I am able to say that, while private opinions expressed by the Popes may have been heretical, or at least materially heretical, the Papacy itself has not issued formal heresy while invoking infalibility. Hence, I hold that the current Church in Rome IS STILL the Church of Christ. We differ in this, I know. I haven't read the book you mentioned; I avoid books which expound a sedevacantist position. I consider them to be a grave danger to my Faith and would not in conscience be able to read one without at least putting myself in the occasion of sin. I'm sorry if that offends anyone, but my soul is my responsibility and I do not wish to put it in peril.
I also know a little about the times of the various antipopes and the widespread distress amongst Catholics at the time. Even some Saints did not know which side to stick with, due to the turmoil of confusion. In times such as those, God does not condemn people because they mistakenly pick/reject the wrong/right Pope in innocence and with a true desire to discern the truth. The information available to them, misleading and misinterpreted, led them to make innocent errors of judgment. That is why I hope and pray that the sedevacantists, acting in good faith and with the best intentions, are still pleasing to God despite their rejection of the Pope and that as soon as this blasted mess gets sorted out holy unity and peace will once more return to the Holy Catholic Church. May the Immaculate Heart of Mary triumph.