I totally agree with Doug. You need a custom converter mainly cause you have a mis-match of parts. Way too much cam for the compression and stock heads for one. There are several good converter companies. Ultimate is one, PTC, Dynamic, are just a few you can send in all your information on your car and they'll build you a custom unit that'll work properly with your car.
Oh yeah, a 904 will do fine if properly built (meaning a billet converter, more clutch discs, etc). And I'd find a low gear set for it if it were me.