Need a break from these brakes... and help

[67chevy_hotrod]

Ok so. 69 chev longhorn c20. I ditched the eaton and put in a Dana 60 out of a 72 GMC(thank you randy500) Everything on both trucks was stock, stock. I just put power breaks on my longhorn and adjusted the brakes. Now one or the other on the rear will lockup at about half pedal. Regardless of adjustment, regardless of road condition, that same side will get smoking hot after a big hill even with minute breaking. However if you back off the pass. side brake the driver side locks up and visa versa. Now just recently ive replaced everything front rear and booster obviously. I even had the rear drums turned! ( new they where both over 12 thousandths out...) do I need a proportioning valve? Is the fact that the 72 (I thought was front disc), mean that the brakes on this rearend in stock form work properly with front discs only?? Has anyone encountered this issue? Thanks in advance!