From memory I believe the 4x4 rear brakes are a direct swap for the 2wd setup, just need to make sure you get a set of 4x4 vented rear discs and a pair of 4x4 rear calipers.

Disc size on the front will depend on what type of 17 inch wheels you have. On my 4x4 I have 17 inch OZ super T wheels and I have 330mm discs with AP 4 pot calipers (CP5200 caliper). Think you can get bigger discs / calipers behind Compomotive 17 inch wheels but not 100% sure how big.