Ok I was misunderstood on what a proportioning valve did. So for the fronts, id just need a T fitting after the valve to go to both the fronts?
And then the rears just run straight to the distribution block on the rear axle?
Yes, sort of. And at the same time maybe no.
I can't remember off the top of my head if the GMT is a left/right system or front/back.
Meaning: there are two chambers in the master. Depending on how it is setup, a chamber may feed the fronts or backs or it may feed front and back or left and right. Its done this way for safety. If you pop a brake line or so ethjng similar happens, you at least retain some brakes to give you a fighting chance to get the damned thing stopped.
This is where the brake distribution block comes in. It distributes the pressure to the appropriate brake as originally designed. The proportioning valve is usually incorporated into the distribution block by OEMS because it is an effecient (and cheaper) way to do it.
This is pretty much how all pre-abs vehicles were plumbed...well, until you get into 50's-60's vehicles where they used single chamber masters. Those were the dark ages for braking when they used single masters and front drums.....