That old compressor is way older than I thought, 1947, weights almost 700lb. They do not build them as they once did.
The single phase 3hp 184t frame motor works. I looked those up the cheapest one I can find is sketchy and nearly $500. Keep! The tank has a couple of pin holes. One was brazed the other was JB welded. I'll grind the JB weld off and do a more proper repair then take it too the fire safety place and jave them test it. One of the 3/4npt nipples broke off and I messed up the threads removing it I'll weld in a new one, a stainless steel step bung. If the tank passes I'll cut the legs and mounting plat from off rotate the tank and reweld that way any water that collects is sitting on relatively fresh metal and the thin spot shouldn't see any water. The gigantic compressor is a devilbliss model 225, minimum speed 300rpm, max speed at 150psi is 550rpm. It seems to work just leaks a bunch of oil. I'll F with it some day.
Not going to recommend this for anyone to try, but I have hydro tested tanks by filling and then running the pressure up with a pressure washer. Last one was an 80 gallon upright that I tied to a tree and stood on the other side, put it up to 300 psi.
NEVER repair an AIR pressure vessel. Pin holes indicate the rust has taken over the inside for the tank. We in the compressor business have seen several of these bombs put in service and severely damaged the people around them. The best thing you can do with that tank is turn it into a barbeque or forge, anything but a pressure vessel. I know you won't listen but I have to issue this warning never the less.
I have hear the rings occasionally fail on these engines. Nothing a set of high quality Toyota made ductal iron rings coated with molybdenum plasma can't fix. S92016-STD Piston Ring Set Standard Size Piston Ring Set For 04-10 Lexus Toyota Camry ES330 Highlander RX330 RX400h Sienna Solara = 88mm rings for predator and others.