I think the guys over at Vintage Wiring of Maine will customize a harness for you, maybe leaving out uneeded circuits, M series end terminals left off for the gauges and lights, add in wiring for a 12V alternator, etc.
Otherwise, maybe a CJ-5 harness could be adapted?
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
USMC Tanker (1811, 1812), 85-93
ASE Automotive Master tech, former Chrysler-Jeep Level 4 Mastertech, CA state EA smog license