Pin C should be constant power. If you jump from there to the distributor, then the engine will run. Does your M38A1 have the floor foot starter switch, or is it new enough to have a starter relay? Floor switches make life a whole lot simple when rewiring.

Speaking of rewiring, was your Jeep an original radio platform? Quick way to tell is that there is a harness run along the passenger, inside side panel, leading to the top of the tool compartment. Usually the harness is gone, but the L bracket mount remains. The reason I ask, and may be incorrect, is that the original harnesses were shielded. If so, you may have fun is reworking the harness. Not impossible, just a pain with the extra shielding added in.