Sand blaster and size of air compressor to use.

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Standard head and valves should work although not as well as reed or plate valves. I thought some about building one but all I have is a 3.0 Ford Aerostar V6 and it's fuel injected so it would be a real pain to convert over, and 3 clinders wouldn't run very smooth. Doing it like you mentioned and using the entire engine for the compressor would be pretty neat and I'm curious how it would turn out. Let us know when you finish up.

350 cu x 0.000579 = 0.203 cubic feet

0.203 cubic feet x 540 RPM = 109 cfm

(4 Cycle engine means divide by two)
109 cfm / 2 = 55 cfm

You will have to do temp. corrections for scfm.
(520 / Outlet temp F + 460 ) * cfm = scfm and would be roughly 35 to 38 scfm "if" the discharge was around 300 F.

It will be running at 11 ratios if you use 150# which means it's going to build lots of heat but your water cooled but will need some sort of air cooler.

Hp = 22 hp * Ratios * mmscfd (million standard feet per day)

50cfm * 60 minutes * 24 hours = 72,000 cfd

22hp * 11 * .072 = 17.4 hp.

That formula is using teflon rings, 2 cycle, and reed plate valves so the auto engine will be much less effecient and will use slightly more HP. I don't have the actual HP formula for air compression.

Very workable, someone care to double check my math?

Using a standard 350 cu inch motor, you will always draw in 129.8 cubic feet per minute of air at 540 RPM, which when you multiply by an Isothermal Constant (located in Machinery's Handbook 25th Edition), to maintain 90 PSI, you would require 16.35 HP (no jacket cooling). Temperature will cause some big problems if cooling is not done and compressor is run for extended periods of time.

I have a friend who made a setup on three-point frame for his tractor. He used a small diesel engine with intercooler/turbo and an electric clutch - all salvage parts. He basically used the intercooler/turbo to preload the cylinders with air, which translates into more efficient and cooler air supply output, and rigged a pressure switch to the electric clutch on the pto to run the engine when pressure drops occur, etc. He ran the pressurized manifold into a 50 gallon tank. The thing was enormous and he used it extensively in his construction business. The horsepower calculation is also located in Mach. Hanbook, but it is much easier to just use the chart.