T-56 build?
There's a big difference between 400 and 500 rwhp. Your tranny will be fine for 400, but maybe not for 500.
We really need more info on what you intend to do. Is it going to be a 500 rwhp NA monster with a 9" rear running slicks? Is it going to be a 400 rwhp DD that will keep the stock rear and street tires?
Give us some more info, and I'm sure we can help you out.

