May have finally sorted my less than stellar brake performance...

[FLYNAVY30]

Stops better in hi vacuum scenarios as you described, but still requires a boot load of pedal. I got the '73 and later booster mounted today....required some modifications to the bracket, but nothing crazy. Now I'm waiting on an adapter for the pedal push rod because the rod in the booster is 3/8-16 and every aftermarket push rod is 3/8-24....nothings ever easy! Hopefully the dual diaphragm booster will net some improve braking. It would make sense since the '73 and later trucks came with 4 wheel disc brakes.