[dsraven]

a hydroboost works really well whether frame or firewall mounted. they require a pressure and a return line to the power steering pump but they are very relioable as far as boost and also quite a bit smaller so tidier, in some respects (there are those hoses).
a vac operated booster usually uses a pivot to operate the acutal booster section so, depending on the mount of the actual booster to the mounting bracket, i am sure you could make it fit to a new bracket for firewall mounting. post up a few pics. if you look back you may see the booster was from a firewall mount originally and simply remounted to the new frame bracket (usually there are 4 mounting bolts). small boosters like the ones sold for frame mount kits are usually a dual diaphragm style to allow the same amount of square inches of surface on the diaphragms for the vacuum to work on.