You are going to want to look for 94 up M6 T56 but even that is only rated at 450 Ft lbs max. There are some upgrades you can do to make them stronger. In most cases it is a lot cheaper to get a automatic that can handle higher torque.

 

I've got a couple friends with stock T56 trans in their older hotrods, and they're very happy with them. But neither are drag racing them. I put a T56 from a '95 Z28 in my buddy's '69 Nova with full roller 355 last year. He's running some pretty large 325-50-15 drag radials in the rear, and so far it's good.