Here is a pic of what I believe to be a Bendix booster and master cylinder combo that I pulled off of a '71 3/4-ton C/20. It has the two cross-wise m/c cap clips, larger yet shallower m/c reservoirs, the larger front line/smaller rear brake line set-up, and, looking at the front of the booster, has a 4-lobe stamping as pictured in the lower right corner of this
page. It also appears to be a larger booster from what I've seen, being about 10" in diameter and about 5 1/2" deep.
I'll feel a lot better if someone can confirm or deny. I've read of incompatibilities when mixing between Delco/Bendix and 1/2-ton/3/4-ton stuff, so I want to be sure before I start rebuilding.
As always, thanks for your input!