Have you tried contacting
@DoctorDiff about his rear brake kits? I know he offers his front disk kits in the 5x4" pattern as well, he may do the same for some of his rear disk kits. You'll get far better parts and service from DoctorDiff than from PirateJack, if he sells something that's an option for you. His prices may be a bit higher, but so is the quality of parts you'll receive.
As for the rest of it, you master cylinder will work with the residual pressure valve removed but you may find you want a different bore master cylinder to better match the pressure and pedal requirements of the new brakes. Same for the proportioning valve- the stock valve should work, but, you may have better results adding an adjustable proportioning valve to better match the new braking capabilities.
