Engine Driven On Board Air from Kilby Enterprises
The OBA compressor is going to be driven by a short belt that runs from the alternator. You have to pull the alternator out and swap out the pulley. Eventually, you will have to remove the stabilizing bar that runs from the firewall to the front grill. (The green bar in the photos) This is probably a good time to do that.
There are 2 bolts and a few electrical connections that you have to remove to get the alternator out. Try not to stress the electrical connections as you remove the nuts that hold them in place.
The large nut in the center of the alternator pulley has to come off in order to swap pulleys. This would be a good time for an impact wrench. If you don't have an impact wrench you can use a vise to hold the pulley. The old pulley will not be reused so it won't hurt to put a bit of a bite on it in a bench vise. With the new pulley in place, reinstall the alternator and reconnect the electrical. Torque the mounting bolts to 41 ft lbs but do not tighten the serpentine belt, yet.