what should i get and where should i get it

i wanted a Richmond from jegs but the wait list is into next year

im building hopfully close to 600 lb ft / bhp

 

There is quite a bit of info on this site about replacement transmissions. There are a couple of performance T5's. One by a company called G force I believe. The main thing about the T5 is its weak case though. A lot of people go with a Tremec TKO 500 or 600. (I have the TKO 600). They are rated for 500 ft-lbs and 600 ft-lbs respectively. They also require a conversion kit. Mine is from Forte's Part Connection. Another option is a built T56 that other aftermarket companies build.

BTW if you get any traction at all your rear end is going to explode just like mine just did.