A friend has a Mac air compressor, model ACP680V, don't know how old it is. I can't find anything about it online. It's an upright model, specs are 80 gallon, 175 psi max, 19.6 ACFM @ 100 psi, originally had a 6 HP motor. Don't know if it's a single or dual stage (how can I tell?) The motor...