disc brake pre72/post73 proportioning valves

I've noticed the "texas" valve on my 73 Charger looks identical to the one on my 87 5th Ave, which is also identical to all the late 90's Dakotas and Rams I've been looking at in salvage yards.

No idea if there's any difference internally, but I have a friend who says he has used late model truck m/c and prop/dist vlave to do disk coversion on 60s and 70s cars.