Just got off phone with M&H Electrical Fabricators 1972 Demon

So I am getting ready to do a restoration on an early 1972 Demon 340 4-speed in my shop and calling about harnesses seen on Yearone. They are made by a company I've used before called M&H Electrical Fabricators. www.wiringharness.com I've had good luck with their product. Nice connectors, accurate and properly sized- no short ends. Wrapped properly too.

So this car is Sept 16th, 1971 build date. The harnessed they list for the dash are listed:
HU319A - after Nov 1971 or HU319B- Before Nov 1971.
Build code N23 Electronic Ignition car.
I figured it was for electronic ignition but its not.
The difference is seat belt warning connectors for switch in the seat (at rear lamp connector left kick panel) and the dash harness includes an extra wire for lighting the bulb on the dash and the warning buzzer.
Just thought I would pass that along as Search showed nothing on my end on FABO.

Also, for the record, they will not answer any emails about technical info- you have to call them. They only answer calls regarding their harnesses so have your part number from Year-one available. They do not sell direct only thru a few vendors like Year-one. Really helpful folks.