Wiring Mess [88' Dodge W150]

My tow pig has decided to stop starting. You can hear the starter spinning, but it does not engage the flywheel. (Bendix is not stickin' out) I have cleaned and replaced every connection from the starter to the battery to the ignition, replaced and cleaned grounds. I took starter off and bench tested it, worked flawlessly. The starter solenoid is built into the starter, and not in a way that I could bridge the gap with a setta pliers. It's a crapshoot but any ideas on what I'm missin'? 318 throttlebody injection.

How are the teeth on the flywheel/torque converter?
You could also just run a jumper to the solenoid from the battery or jump the starter relay on the fender.

That's either a busted starter drive, or a flywheel with teeth missing.  

Bar the engine over a half turn and check again?

It's the starter.  Just because it works on the bench doesn't mean it works when under load.

The overrunning clutch is probably now a bidirectionally overrunning clutch.