Rear Axle, Which Method for Bolt Pattern Conversion...

What Bad Sport said. Find a BBP 7.25 and just swap the rear axle. BBP 7.25's are usually pretty cheap, just gotta find someone that's upgrading their rear axle. They started in '73 though, any 73+ disk A-body would have one. Pretty good odds they'd have a 2.76 rear gear too.

As for the strength, in a /6 street car it should be fine. You could upgrade it to a Sure-Grip if you were concerned about it, that strengthens them some because of the way they usually fail.