The later trucks and some of the 3 ton trucks with dual master setup did just what OldSub suggest using two hydovac units one for the front and one for the rear. I did what Grigg did with the hydro boost system pictured here with the bracket that mounts it on the inner frame rail using the stock pedal assembly. This unit came from ABS Power Brake.
http://rides.webshots.com/photo/2701798080096773078qEsBli That's what my 1970 C50 has from the factory.It has a duel master cylinder going down to 2 hydrovacs under the cab. One for front, and one rear. Idon't know if this is really practical for a retrofit. I think they used this system due to the fact that these trucks were not running power steering, and the hydroboost was not available yet( to my knowledge ) I would think that you could adapt a hydro boost if you wanted to add a pump, or get a large vacum booster.
