Proportioning valve

[1970Tex]

Hey guys, looking for some help sourcing a GOOD quality proportioning valve. 1970 half ton, 2WD, front disc conversion, manual (no booster).

Finally got my truck off the lift, and i thought i would be off to the alignment shop, but low and behold the brakes were extremely weak. Firm pedal but not much bite at all. Tried bleeding the brakes (with home made tool to keep P.V. shaft centered) and barely anything coming out the rears. Bench bled MC, tried again, still nothing. So i figured the P.V. must be stuck. From what i can read, you should be able to slide it one way or the other with a pick. After removing the P.V. assy from the truck and dismantling, the valve moves extremely stiff. Basically i need to force it with a punch to get it to move.

Ordered a new PV2 valve from Amazon, you know, the ones for $50 made in China and was lured in by 2 day delivery. Everything looked good until i installed it, and found out it leaks. Of course its the special 7/16-24 UNS threads for the rear input. It seems like they didn't tap it deep enough, but after inspecting farther, i measured .240" from the top of the valve body to the top of the flare on the new one, and my old one measures .208".

So I'm thinking with 2 P.V.s i should be able to transfer the piston from my new one, into the body of the old one...Nope. Won't slide at all.

I give up, ill call this a wash (and a good lesson). Where can i find a good proven possibly made in USA valve?