All I can say for certain is that with just the MC pushing by brakes, it was a real bear to get it stopped if I needed to do it quickly. Lot's of pumping & swearing involved. The boosters push more fluid than the MC as well, so help more than just how hard to have to push the brake.
Something you might do is mount a vac resivior tank under the cab (thinkin of doin this one myself actualy) and if the engine isn't doin it well enough you could get either belt driven or electric vac pumps to keep the booster ready to go.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P