Corvette = strong, but not good for twisties unless you do the late model stuff. There is too much potential for slop in the "upper control arm" (i.e., halfshaft) and when the diff gets worn camber really starts to get unpredictable.
Tbird = really strong and better. Much more common too. Super Coupe would have the 8.8 trac-loc rear, most other Tbird-Cougars got the 7.5"
Your car nor your wheels care what shape the springs are - leaf or coil. Leaf springs are bad when they're holding up a live axle, but the live axle is much of the problem there... The fact that leaf springs don't have much side-to-side locating ability nor torque control make them terrible, but in a Corvette or Cobra, they're just fine. I don't see DeDion tubes anywhere in this thread, though. What are you smoking?
760 = quite weak, probably. I don't actually know HOW weak it is, but the axle stubs are MUCH smaller than a 1030 axle is: 26 versus 27 spline, and probably 1/8" smaller in the diameter.
Stick with the live axle gets my vote. Put a 240 axle in there with a true trac and it'll be strong enough for a whole bunch, and be lighter than just about anything else.
