I don't know if this is true for 50's-60's trucks, but my 43 G506 1.5 ton all I have to go by.. that said:
I think the biggest obstacle to using a late model dual vac/booster is the brake pedal geometry. Modern pedals are hinged at the top whereas early trucks have the pivots at the bottom. The amount of linkage kung-fu needed to put a large diameter power cylinder where the stock pedal can actuate it is gonna be a challenge.
Whereas simply adding a second canister to the other frame rail and some plumbing to split the front/rear would be trivial. You could even have an 'emergency cross over' rigged up.
I'm really debating the dual vacs on my G506. I want to, and for the small amount of 'non-stocky-ness' it would add I like the idea of stopping a lot more.
