Well, an engine-driven approach will work, and I can see myself fabricating brackets to work with the OEM belt system or an add-on pulley. There may even be a Dodge or Dakota truck pulley system that would work here, this is essentially a Chrysler LA V6/V8 engine design. I'm envisioning decades of 318 and 360 industrial strength engine applications that might be out there...Kilby Enterprises has goodies for York air compressor systems, including a bracket kit for the V-10 Chrysler engines. You might look at the Kilby parts available and see if any would work with your Dakota 3.9L V-6.
If you go it yourself, work would entail aligning and balancing the pulleys, using the right York compressor (they mount upright or horizontally), addressing the belt load to assure reliability, correct hardware, adding a reservoir and plumbing as you describe, and so forth. I would not mount to the vehicle frame, as the engine moves in relationship to the frame, and belt tension would be impossible to control. Onboard, engine driven means engine mounted.
There is an alternative, and I have it: a York compressor powered by a 12V motor. This unit was commercially built, and I looked online for the supplier without finding a listing. (If this sounds appealing, I'll take photos, share more details and research current sources, if any.) The entire setup stores in a sealed military canister. I have the available add-on tank.
You take the compressor unit from the canister and use an Anderson plug to connect to your vehicle's high amp battery source. (Warn supplies Anderson plug cable kits to 20' length.). The compressor can be hooked to either end of the vehicle if you have heavy Anderson connectors at each end. This provides York-grade air volume and also the option of a reservoir tank for reserve when running air tools.
On this same note, ARB now offers the twin-compressor system for 12V, higher volume air supply. Though certainly not an industrial strength York compressor head, this will handle light air tools and can be used with a reservoir, too. Imagine: You get to hear two ARB air compressors talking to each other at the same time!
There are also other 12V compressor solutions. This is an option to engine mounting issues and does reduce vehicle fuel consumption, the same principle as a Ready Welder versus an onboard, engine driven frequency welder that puts a good load on the engine's high output alternator and burns fuel the whole time you're welding. There are pluses and minuses to both. Think of the electric compressor systems as something akin to a diesel-electric locomotive: The engine is simply running the alternator for a battery supply system; the compressor is electrically powered.