The 1947 - Present Chevrolet & GMC Truck Message Board Network

you could run a nice big vacuum reservoir down near the booster, out of sight generally, and see if that is enough. do a few big brake applications and see how the vacuum holds up. go from there.
you could run a vacuum pump after the truck is test run and you find you may be low on vacuum available. just ensure to leave room for it somewhere.
will you run vacuum wipers or anything else vac operated? you know the wipers slow down or stop when going uphill and the throttle is wide open and then go crazy fast when going downhill-throttle off-but they don't have a reservoir so run directly off the manifold
trial and error I guess. build it, modify it to suit your needs if you find it isn't as awesome as you thought.
you could also run a hydrovac booster mounted remotely and use the stock master cylinder to operate the hydrovac. it is what a lot of midsized trucks used for power brakes. when you step on the brake pedal the original master cylinder puts pressure to the hydrovac unit, mounted remotely, which operates the brake booster and applies the (usually) larger master cylinder on the hydrovac unit to operate the brakes. a single brake line is required from the original master cylinder to run down to the hydrovac unit. the hydrovac unit would then have the tandem master cylinder and proportioning valve set up. they were even used on the caddilac and others back in the 50's. the tough part may be finding one that uses a tandem master cylinder. you could google it for more info if that interests you
or, just install a vacuum pump and be done, lol.

here is an old video, for nostalgia's sake, explaining how the hydrovac booster operates. takes you back to high school when all the videos seemed to use the same narrator, haha.