Proportioning valve issues with disc swap?

[MoparDealer1971]

I installed the disc brakes from a 1976 Dodge Aspen station wagon (V8) on my 71 Challenger.  They are the smaller 10.5in I believe, not the larger C-body rotors.  I simply installed them, no booster, no proportioning valve.  As of now the car stops fine but it seems like the back brakes grab more then they should.  Would this be because of the drum/drum valve?  For example, I cannot power brake.  Yes, I know, this means I need more power...I am working on that.  But I was pondering it the other day...maybe its the brakes!?  If I come down on them HARD the rears lock first.  So, I guess these are my questions

Would the drum/drum valve cause uneven pressure with extra going to the rear?
What are my options for a new valve?
What are my options for later model or other conversions for power brakes?
From what I understand I can go up to the C-body rotors by just getting caliper mounts and the larger rotors...its this true?

Thanks!

[dodj]

Rears locking first is pretty much the norm for these cars. You can put an adjuster in the rear line or replace the whole prop valve with an aftermarket. Brads70 put a wilwwod adjustable prop valve in his car.

[MoparDealer1971]

Rears locking first is pretty much the norm for these cars. You can put an adjuster in the rear line or replace the whole prop valve with an aftermarket. Brads70 put a wilwwod adjustable prop valve in his car.

I think mopar might have an adjustable available as well.  I will look into that.  I suppose you set those by feel or is there some sort of method?

Anyone ever put a later model power booster on?  The period boosters are sorta hard to find and $$$.

[Chryco Psycho]

http://www.cuda-challenger.com/cc/index.php?topic=85620.0
 CHECK HERE Brad show the proportioning valve he used , you also need to remove the residual pressure valve from the master , it is behind the brass insert the flared line seals against , I use a threaded screw to pull it out with vice grips & then re-install the insert once the rubber valve is removed

[dodj]

I think mopar might have an adjustable available as well.

My local mopar dealer sold me the Wilwood adjuster.