i know of a bunch of evos running lots of power on the stock tranny and driveline. clutch and flywheel definatley need to be replaced. from my research, the cusco or exedy (both the same) hyper twin disc clutch is the primo clutch. it comes with a lighter flywheel and utilizes your stock throwout bearing. Also, to improve your driveline, a quaif limeted slip for the front. i know
www.roadraceengineering.com sells the diffs. That diff will save your transfer case and you alot of money in the long run. Also, i believe the driveshaft shop has been workingon front and rear shafts for evos, you might want to check them out, or some other place to get high power driveshafts. but the tranny and diffs should hold up some pretty good power if your not breaking the hell out of them... the dynoflash.com evo (big AL!!!) was running 600+ hp at the wheels on stock tranny and diffs....something to think about.
the exedy clutch (or cucsco) is about $1600 and like i said, it comes with a lighter steel flywheel and retains pretty much stock driveability. Also, is good for feathering out of the whole for high rpm launches.