What to do with an old 3 cylinder compressor?

[Scooter]

I have had a 3 cylinder compressor sitting down the side of my house for years, condition unknown. I pulled the 3 heads off tonight, pistons and bores look good, but the engine will not turn over by hand? (electric motor spins by hand). So I looked inside the crankcase, and there is corrosion? I think it is an Ingersoll Rand, I will get some pics tomorrow. My question is, are they worth repairing? I am going to strip the bottom end and see how bad the corrosion is probably over the weekend. I will also power up the electric motor to test it
(3 phase). Anything else I should be looking at? All I can think of is receiver for rust internally? Any helpful hints would be great. P.S. It is only for home.