Hit up V8 Archie. www.v8archie.com he has several 500hp and Supercharged LSX Fiero's running around using the G6 Six Speed or the 4T65-HD Auto transaxles. Complete kits or just adapters. The trans is fairly cheap, if you are willing to hunt wrecking yards.
6sp auto trans here (6L80) go for 1200-1800USD.. peanuts compared to the T56s, TR6060s etc. But we have far more desire for manual cars vs auto cars typically, although plenty of autos are made, they are just not so sought after by performance/street build level stuff and enthusiasts.