How much power will a Turbo II Rear End hold??

 

It's actualy based on torque rather than horsepower. The amount of torque it can take depends on how you drive the car, and how well the rear tires stick to the road. Drag racing, especially with slicks, is harder on the driveline.

The TII rear end can hold quite a bit of torque. For example, Attila the Fun's 20B-REW RX-7 producing a peak torque of 416 lb-ft at the wheels has lasted over 50,000 miles so far with the TII driveline. Most of the driving was on the street, but the car was also driven in road race events.

 

so with like 500 lb-ft id be out of luck as far as reliability goes

 

Yes, a high-output V8 conversion is probably better off with a very strong live axle like a Ford 9". You can get better input from those who have actually performed a V8 conversion in our Other Engine Conversions forum:
https://www.rx7club.com/other-engine-conversions-non-v-8-118/