unless uve got lots and lots of dosh, it is possible. have a look at this link in supraforums. http://www.supraforums.com/forum/showthread.php?t=221891&highlight=400hp This car has got individual throttle bodies! Loads of money spent.
This has been asked loads and loads of time. loads of ppl have thought they can make this na power machine but everybody have just given up and gone turbo instead. The cost for a good turbo kit ~$4-5k with a T61 run that easily. Bits for that na power: stroker kit, lightweight rods, pistons, pullies, cam gears, cams, xerd headers, remove cats......strip the interior. That is gonna be expensive easily >£10000
Good luck.