76 Scamp A/C

I have a 76 Scamp with the slant 6 and the a/c system on my car has been open for the past 10 years or so and I was wondering about the compressor. It's the RV2 and it does spin by hand, but it looks very brown and nasty inside from what I can see through the inlet on it. I removed the EPR valve and put it back on the car and hooked it up the the condenser and it seems to work extremely well. I poured a bottle of ester oil into the suction port and with the engine idling I was able to blow a lot of brown water out of it, but it's very quiet and doesn't drag the engine down any. When I cover the line coming out of the condenser, it builds pressure really fast and it will hold it. I'm currently getting a new expansion valve and drier, but everything else is original. Depending on what happens, I may have the hoses rebuilt if possible. But now with the question: with what I described of the compressor, does anyone think I'm going to have problems with it? I'm going to hook everything up and vacuum it down to see what happens because of how hard it is to get parts, but I'm wondering if it'd even be worth the Freon to see if this thing will cool down. From what I was told, the compressor was removed to replace the water pump and put a new head gasket on the engine, but was never put back on.