I believe this is what they were talking about, in your original post, for an adapter. Connects a cowl mounted wiring harness to the newer style, round plug, found on later (but still old by today’s standards)) control boxes.
https://www.ebay.com/itm/272805319103?hash=item3f8476d1bf:g:f0cAAOSwopRYdqYA
Long live American manufacturing!
