Sorry to take so long, but I was in the middle of a response to you when my provider shut down to change their equipment - but back up now.
I have a PTO pump (not what I would call an air compressor, but that may just be because it doesn't have a tank). It works very well for pumping up tires in the field. It is a single piston with a crank and connecting rod, slips onto the PTO shaft and pumps away. Don't know the cfs (?) or the pressure, but guess it would depend on the condition of the rings on the piston.
Is this what you have? Mine isn't close or I would take a digital pic and post it.