I've got 4 wheel disc on mine, are the rears needed? Nope, just fronts would have been just fine, but I was young and had money burning a hole in my pocket, and I got a nasty, not so fun ride thanks to the death trap 1 pot master cylinder... used SSBC's kits, A156-2 in the front and A155 on the rear...
I rebuilt the front end w/ a PST kit while I was at it, and changed the left handed lugs in the rear to right handed (be careful not to beat the hell out of the axle flange when putting the new studs in) but the swap is really, really easy.. hardest thing was bleeding the system out afterwords, well, that and hanging upside down while getting the old master out
Summit's page for it says 14" minimum, however, the 14" steelies WON'T CLEAR the calipers, but factory magnum 500's will