8 3/4 Help and Opinions?

First, I've seen a few fast cars with the small u joint. But they were automatics. You can change the companion flange without any problem.
Go ahead and change it now. Use either the big joint or the 1350. both will work. If you are going to buy a new driveshaft, buy an aluminum one. They will be a little more cash (but not that much), but there'll be a performance increase due to less rotating mass. good luck.

don