just wanted to point out the mkiv uses 320mm front and 321mm rear rotors. the rears are ~1/2 the width (16mm) of the fronts (30mm).
if i had to get a bbk, in terms of bang for the buck, i'd use the available mounts for the supra fronts, and use ucf20 Lexus LS400/Toyota Celsior calipers.
dirt cheap if you know where to look, BIG BIG advantage in unsprung weight (2pc alum.) and a grand loss of 5mm, fronts are 315mm. plus they've been used by the SC and GS guys for years now and can take the abuse. oh, and they're 4 piston calipers with ~same piston area as the JZA80 turbo front calipers.
now if i could find a machinist i'd be tempted to maybe get a certain set of 315mm front rotors with monoblock aluminum calipers (4piston) to work....