The Chevy 1/2 ton is around 11" wider than the 3/4 ton. If that is a fact with the GMCs it wouldn't matter for the break MCs or adding a booster.
However my experience with brakes is after the 216 and 4spd tranny has been removed. A booster might interfere with the clutch. Someone with that experience will drop by soon I'm certain.


~Jim