Widowmaker, I'm in the middle of putting S4 RX7 calipers and big discs onto an AE86. Might be a bit more expensive than you want to do, but if you're interested I can send you all I know about it and dimensions for adaptor plates and all that junk.
That's assuming I ever get it to work.
I don't reckon you should bother with the rear either.
Hen