This is a fixed-displacement Harrison R4 compressor sometimes found in GM cars and trucks. It can be used as an air compressor, but it’s not necessarily the best. Why? Lubrication. It’s difficult to take a Harrison R4 apart, so greasing up the internals is not really a solution. Instead, you have to run a tool oiler on the intake and an oil/water trap before the tank. We have one in our ’49 CJ-3A running a late model Buick 231 V-6 that only has a few hours of use on it. We are not sure how long it is gonna last, but we oil it frequently through a T-fitting on the inlet and run an inline tool oiler on the intake. We’ll let you know if it lasts or was a waste of time after we get some more time on the compressor.