I'm getting the feeling that you are thinking of the Hyd0-Vac, rather than the Hydo-Boost. The Hydo-Vac was the original style power brake system that was used on GM trucks starting in the mid '50s, and did mount under the truck or on the frame depending on model. It is a separate booster, but it was still a vacuum operated system. There is still a similar system available in the aftermarket made by Midland. They Hydo-Boost simply replaces the vacuum booster with a hydraulic one, run off the power steering pump. If this is the way you would like to go, I would suggest getting the M/C mount that gooes in the stock location under floor, and use that booster, perhaps run with hard line. One from an Astro Van would be the best bet, as is rather compact compared to the full size truck version. Get the pump as well, as they are different form the std power steering pumps (if you plan to have power steering).
