no popping on acceleration with most of the lower studs broken? hard to imagine.

I bought a 78 SC with 8,484 miles. It was last licensed in 98 or so. Had the popping sound and all 12 exhaust head studs were broken. Engine was removed in less than 4 hours and dissembles that weekend. Hardest part was getting the broken studs out. Use heat and vice grips. Hopefully enough left to grab. No other damage. Put in upgraded tensioner. Once I had all studs out and all gaskets in stock, I spent about 35 hours re assembling, measuring, installing etc. I would remove the transmission with the car. Be sure to use Locktite on the axle shafts to transmission flanges. Ask me how I know.
Ask many questions. Folks on the board are great!

New schnorr washers and running small rags through each hole, last one with brakekleen on it so the bolt threads don't pick up CV grease works as well.

I think backed out bolts are mostly due to greased threads and worn washers.

The definitive thread, with lots of Grady:
http://forums.pelicanparts.com/porsche-911-technical-forum/222537-reconstructing-constant-velocity-cv-joints-12.html

Good luck lespaul. If you hit snags there are plenty of 802 Pelican's who can help - I also just completed a top end job in the spring of last year. Plenty of helpful knowledge among members here eager to share.