I have a very similar control connected to 1974 140, although it is not the helm mount type, but rather a starboard side mount where only the arm is outside the side panel. The portion behind the panel, looks very much like yours. Over the years, I bought a couple of old ones on eBay, as well as a complete unit from Seaway Marine, seaway marine.com. They have lots of NOS parts from this vintage. It would be well worth the time to check with them for your part. I still have the old units laying in my stash, but it is all in my shed up at the lake, far away and closed for the winter, which does you no good right now. I do recall the part you are describing being easy to lose, and I had to borrow the piece from the stash to put on the new unit.
I was looking for an overall model # but it seems like it isn't clearly marked or the label is gone. Found casting # 380 37607 which is a cam part # inside the unit. Thanks for the link!
Well thank you for getting carried away because now we are both a step ahead! I am going to shop around and see if I can find a parts binnacle like you did, seems like a good idea in case I lose any other parts! The thing was connected and apparently fell out somewhere when I was bringing it inside so seems like keeping a spare onboard would be a good idea too. The tiny clip I have has hardly any tension on that pin at all so maybe they were both just worn out and about to fall out on their own.
