The main difference is in their torque capacity. The AW70 is meant for the lower torque normally aspirated engine, while you can think of the AW71 as a beefed up version suitable for the higher torque of the turbo-charged red-blocks.

If you're also replacing the torque converter, for the factory original setup there's probably also some difference in its design specs in terms of stall speed (to be suitable for the turbocharged engine), although I'm not sure about this (it would make sense).

But basically, these trannies are the same except for rubustness.

Although you didn't ask, if you're looking for a swap from a pnp you should know that there's a big difference, though, between these and the AW71L, if you're lucky enough to find one. That "L" means that it has a lockup torque converter, which eliminates fluid coupling slip and improves fuel mileage (but only on the highway, when the lockup engages).