I have a different abs system than you but when i was researching bypassing mine it looked like it the valve would just go on the rear circuit and the fronts would go strait to the master. If you go with the actual proportion valve with warning switch then you could run dual circuits for the front.
Clamp off the flexible lines and see how the pedal feels then remove one at a time and see how the pedal feels.
What is the year and model of the truck?