Achieving proper brake balance

[JLM]

Now that the car has been on the road again I began to start testing things like brake balance etc.

Currently the car is setup with an MP Brakes front disk conversion with power assist brakes. It is running the factory proportioning valve with factory rear drums at the moment. I will eventually switch to a rear disk setup but that will liekly be down the road when I go to a more worthy front disk setup as well.

Problem right now is that the rears lockup very quickly. Is there a way to control the amount of pressure going to the rears with a factory style proportioning valve? If not what is a recomended unit that would work with both the drums I have now and a set of rear disks for the future?