What type fittings on I gen w126 AC condensers?
 

I have a spare condenser and want to hook it up between my shop compressor motor and the tank to try and get better control over the moisture in my air supply system.

An original GM R-4 compressor should be o-rings. Most replacement R-4's were the later style flat washer seal with a gasket in the middle of the washer that a spacer went through. So you could have either set-up, it depends on whether or not it's original or a replacement.

Hope this helps.

At what point do you plan to remove water, and by what device?

Ha! Looked again, OP was asking about condensers NOT compressors...oh well.

A simple water filter with a drain at in the bottom of with a clear bowl.

I expect to get much less water in my air tank and will deal with what comes from the tank with an old fashioned cool can, gal of frozen water, 20' coil of 1/2" copper in a 5 gal bucket of water. In at the top, out at the bottom with 1/2" X 2" pipe, a tee, hose connector then a 1/2" X 12" pipe a 1/2" ball valve.

After that a good filter system for the oil and moisture vapor which is more stubborn.

Here's a shot of the connectors I need to transition to a standard pipe thread to connect the unit to my air compressor.

I knew alot of refrig. men use grain alcohol, to grab moisture from systems

Those fittings are called male "O" ring AC fittings you will need female "O" ring fittings to connect to them. Those early vintage condensers will be SAE threaded fittings.

You will probably need to cut one of these and solder a pipe fitting to the other side or make a hose with and AC fitting on one side and a pipe fitting on the other.

https://coldhose.com/collections/female-oring

Yes Sir, I spent a couple days trying to save those connectors somehow and gave up two days ago. Unfortunately the larger tube is a 5/8" OD which was quite difficult to find. I finally found a 5/8" solder fitting in a tiny mom and pop hardware store. The smaller tube is 3/8", much easier to deal with.