Brake bias requirements are highly variable. There are way more factors then "I have disks" or "use part x from a vehicle with 4 wheel disk brakes". Such factors (but not all) are; bore size (mostly calipers), rotor size, pad material, weight bias (hard top or not, what engine, spare, bed packed with spare parts or not, how heavy are the bumpers), center of gravity (taller truck will swing more weight to the front axle under braking), that is also dependent on wheelbase (long wheelbase won't shift as much as a short wheelbase), and even suspension tuning. All this stuff goes into how the tire is loaded against the road, thus how much traction it has, and that dictates how much braking it can have, which is controlled by the size of the brakes, size of the calipers, pad material and ultimately the pressure in the brake system that is applying the whole mess.
Really the only way to know if it works is to go out and drive it and see what happens. If it is well balanced, you are done. If not then there are a lot of ways to get the system more into balance. You can play with pad material, center of gravity, add a heavy bumper (or take one off the front), and ultimately play with a proportioning valve.
A proportioning valve is not a good way to take a lot of brake action out.
Scenero;
lets say a good brake system has 1500 PSI at all 4 wheels for good braking. The driver can modulate that pressure as needed.
If the rear brakes are crippled to 900 PSI and the fronts still get 1500 for it to stop well all appears good, right? Wrong. What happens when the driver presses a little too hard and locks them up. Lets say 1600+ front and 1000 rear. OK the driver has to back off the brakes to unlock the wheels. Once a wheel locks you have to go below the threshold pressure for it to release (you can search out static and dynamic friction from your physics book for more details). So the fronts need to back off to say 1200 PSI and the rears to 700 for the wheels to release. The problem with a prop valve is to lower the regulated pressure you have to go below the inlet pressure. Brake fluid is in a closed system. you can't vent the rear pressure back to the master cylinder until the supply is lower then the output. So the driver will have to lift off the brakes to no more then 600 PSI to get the rear brakes to unlock, which is less then half the pressure for good front braking. Too much rear brake with an aggressive proportioning valve is a bad fix. I only like to see a proportionng valve used for very fine tuning.