Installing an adjustable proportioner valve

I'm doing another disc brake conversion and this time I want to use an adjustable valve for metering the pressure on the rear brakes. Where is the appropriate place to install it? Between the master cylinder and the block on the frame rail or behind the block on the frame rail? or does it even matter as long as it goes on the rear brake line?
Pictures would help, thanks.

anywhere in rear line, next to master is easy to get to, but you won't be adjusting it often

Can the block that is mounted on the frame rail stay or does it need to be removed. I think it is just the low brake pressure switch and distribution, correct?
It is all original equip and had front and rear drums.

Sounds like a distribution block in which case it can stay. I put mine up by the master cylinder.

Thanks a lot..............

Mine is right up by the master, we just got a small brake line and bent it to work. that way we didn't have to mess with any fittings.
Jim