When you switch to rear discs make sure you don't have a residual valve in the system for the drums (10 Psi for drum, 2 Psi for disc, if equipped) as they will make the brakes (discs) drag.
Some are in the combination valve, some are in the MC, I think by that late of a model year it would be in the combi valve, but it's easy enough to check (hook a presure gauge to that side of the system, lightly actuate the brakes and see what the pressure drops to when released).
