Choppycam

Hi all!
My project is near finish, but I have a big problem with rear brake. No oil go to the rear of the car. I dissassembled the master cylinder and cleaned this one. All is ok. But when was time to dissassemble the proportioning valve, the small seal at the end of vertical piston, stay at the bottom of the hole. So, the seal need to be replaced...

But, I know that Iroc Z with four wheel disc brake have problem with this proportioning valve and I when go with adjustable proportioning valve.

What will be the best choice for me? Do I need proportioning valve for front and for rear brake (2 valves??).

Let me know and thanks in advance.

Cam