You should call up an auto engineer and see what the power/weight ratio also capacity/weight ratio is involving engine swaps, im pretty certain i can put an SR20DET into my RA60 just cos its fairly similar weight to a silvia and also my brakes are damn large, i know for a fact my car pulls up harder than a stock sil.. Not to say you want to go as far as an SR but you could think about a 22RE from an RA65 celica, they hammer, i had one n i wound her off the clock weekley (230+kmh )
Just an idea, if you call up, let me know how you go as i'd be interested to hear what they have to say.. There is a a basic outline guide to it, rules can be bent a lil heh hope this helps a bit,