Power Brakes and Prop Valve for disc/disc setup

[Chappo]

I am going to be adding power brakes via a JB5 brake booster/master cylinder setup for 1980 model, was going to just get a new rebuilt unit from Orielly's.

http://www.oreillyauto.com/site/c/detail/A1C0/501008/01305.oap?year=1980&make=Chevrolet&model=C10%2BPickup%2BRWD&vi=1030543&ck=Search_01305_1030543_888&categoryRedirect=01305&pt=01305&ppt=C0066

 My 80' 2wd has manual at the moment, and my main question is if I go disc/disc do I only need to add a proportioning valve and that's it to handle the new disc setup in the rear?  I will be going with 13'' McGaughy's in front and Blackbirds rear disc conversion in rear with the power brakes.  This is the valve was going to get.

http://www.azproperformance.com/McGaughys-Non-Adjustable-Proportioning-Valve-64090.html

On the other hand, I have had several people tell me that the rear drums will be perfectly adequate for a street/cruisin' setup.

Power will be a 5.3/4l60e for the moment, don't plan on going over 400 whp.

Any input would be greatly appreciated.

[Captkaos]

I would use a disc/disc prop valve or see what Blackbirds recommends.  I have know people using the stock power disc drum combo valve without issue and others have.

Look here:
http://73-87.com/7387garage/chassis_suspension/reardisc.htm