The seller was: nelcohotrods on Ebay. He said this unit was designed for trucks over 1 ton. He has several to choose from. Also the best price I could find. See description below.

1955-59 Chevrolet & GMC truck frame mount power brake unit pedal assembly with 8" dual diaphragm booster with dual well master cylinder. This system bolts directly to the frame and will power any drum drum or disc drum brake system. This system is for larger trucks where ground clearance is not an issue.