'67 C10 6772CT booster conversion issue

Working to get my wifes (new to us) '67 C10 on the road. It had manual brakes, so, I ordered/installed the 6772CT Booster/master package:
http://www.classicperform.com/Instru...PDF/6772CT.pdf


Also went through the brakes to be sure everything was good... It is.


Took the truck out for a short brake test after the install. Got home and found the rear brakes were reeeeally tight. Took the wheels/drums off, and really didn't see anything that said 'this is broke'. Wheel cylinders... maybe?


Replaced the rear wheel cylinders. Moved the truck forward/back/forward/back a few times in the garage, and.... Rear brakes got super tight again.


Noticed the pedal wasn't coming all the way back, and when I manually pulled it that extra 1/2"… all was good. Brakes were free.


I was thinking 'maybe the return spring isn't strong enough? I went in and 'shortened' it a bit so there's actually more pre-load tension on it.


This sort of maybe helped. The brakes seem to not tighten up and stay that way, but, the pedal still isn't returning all the way back to the rubber stop.


I'm 'thinking'... maybe i set the connector rod too short? (in this vehicle, the pin holding the connecting rod to the brake pedal is difficult to install or remove because the steering column is in the way, so I was somewhat 'winging it' on the shaft length)


I took everything apart and went to 'lengthen' the rod on the brake pedal end, only to find out I didn't have the threads left on the shaft to lengthen it. It was already at the end of it's travel!


Thoughts? I'm a bit befuddled here, and would really like to get this beast out of the garage, and on the road!!