Just to confuse this thread some more with a pet-peeve of mine . . .
My '41 fire truck (either 1.5 or 2 ton - not sure which) has a factory-installed vacuum-assist canister for the brakes. In my mind, this is NOT the same as what everyone refers to as a "Hydrovac" - nor was it called such in the factory salesmen's book. Far less complicated, different principal, and different hook-up. Where a Hydrovac can be mounted anywhere on the truck, and just plumbed to the Master cylinder, the Vacuum-assist is a mechanical only deal, that must be mechanically attached to both the pedal and the master cylinder. No brake fluid ever goes to the vacuum assist unit, and it does NOT require "bleeding".
One uses vacuum to push the brake fluid to the cylinders (hence the "hydro"), while the other just uses vacuum to help push the pedal. (gross over-simplification?)
Anyway, this might affect your plans in terms of replacement of the missing unit. I'm guessing your truck, being the same model as mine-ish, may have had the vacuum assist, which mounts pretty much in-line with the master cylinder, just aft of it - if I remember correctly. Guessing a vac. assist would be harder to find. On the other hand, no reason a hydrovac couldn't be installed instead.
How's that for muddying the waters?
-Michael
