the headgasket is not all that difficult, i did mine myself. so do most supra owners. beats paying a shop to do it and you know it was done right...
I've had my car for 2 yrs, just modded it this summer. installed this stuff.
Big upgraded ct26 turbo, Custom IC pipes, Spearco IC, Altered 3000 pipe, 4" K&N, Monza ssqv, HKS fcd, stage 3 pressure plate, Ported head, Intake and Exh. manifold, 3" DP 3" Megan GT. mild mods compared to some...
suprra_girl made a nice write-up on basic performance upgrades, (bpu)'s
http://www.toyota-supra.info/forums/mkiii-faq/50-steps-to-modifying-your-mk3-supra.html