Question about using a 78 3/4 ton master

[Yukon Jack]

I have removed a manual brake master from my 1970 K5 and have installed a master cylinder, booster and proportioning valve from a 1978 3/4 ton.

I removed the donor parts quite some time ago and I don't recall which reservoir is supposed to feed the front as opposed to the rear.

I currently have it hooked up with the front reservoir going to the proportioning valve to feed the front brake lines. I know I have read that our year 3/4 ton truck's have the front brakes fed from the rear reservoir but don't know if that holds true for a 78 3/4 ton.

Any one know? I posted over in the 73-up section but doesn't look like anyone there knows the answer to this question.

Here is how mine is presently ran



Thanks