Brake Proportioning Valve

[au03z71]

So, the original proportioning valve on my '72 is shot. The front brakes work fine, but the rear brakes are getting no fluid pressure. Turns out my proportioning valve is shot. I took it apart, cleaned everything up, put it back together, and re-installed it and no dice... Anyway, is there a cheaper alternative to buying a direct replacement? Summit has them but I'm not sure how I would plumb it. Anyone ever replaced one of these?

Thanks