Doober there's a good & cheap TH350 build thread on Hotrodders.com by Jakeshoe. It's good for 600 HP/TQ. >> http://www.hotrodders.com/forum/th350-rebuild-tech-145361.html
There's a TH400 build thread also.
His site has TH2004R, TH400 etc.. build tips also>> http://www.jakesperformance.com/
The HD Direct Drum w/36 element Sprag & outer Race, T-Brake Vbody etc.. are where the $$ come in.
http://www.atiracing.com/products/trans/transparts/alumdrum.htm
http://www.atiracing.com/products/trans/transparts/sprags.htm