Headline..
Man killed by "Air" Bomb in garage! Man, your asking for trouble here. Think it's better insurance to buy ready made unit myself. Anyway, maybe go to Library and check on books on "Fluid" control or Hydraulics or something to get math formulas and tips on something like that.
Write the manufacturer of pump if a name or model is on it anymore for specs. I bet that pump isn't as big as you think in output. Thats a small pulley on it. You will need the fan or A fan on it to keep it cool. AND, where you gonna get a wide ribbed belt like that? Bet that's outta a ship or commercial system. You have 3-phase in garage, bet not. Most big motors will need that to keep from using all available juice you can make/get on it. Find a body shop going outta business, buy there's. That happens quite often I think. Pump may be a two stage where one cyl pumps up to some pressure and second one takes it rest of way and to tank. You would need that if you have a big tank or it will take forever to fill it. Don't forget safety valve and shut-off switch. What about a water drain valve? Won't be one on Gas tank will there? Can't weld in a "bung" for one with fuel in it to "blow".
Sorry, I don't like this idea at all!

:p
