7 3/4" and 8 1/4" rear weaknesses? (and other ?'s)

Yup, 7-1/4 will break spider gears or crosshaft and bust the spider shafts out of the carrier with not much persuasion. 8-1/4 are actually fairly tough and I would think it would take a bit of effort and some serious torque to break one. 8-1/4 should last in a street car . It's not ideal or the toughest thing you can put in but acceptable.