Guess what this is...

Definitely factory, just can't remember specific application and purpose. I have definitely owned A-bodies with this part in the past, but we're talking 20 or more years ago. Current fleet includes 2 71s, 2 73s, a 75, and 3 76s. None have it. Therefore my thinking it's a 74 only deal, and thinkin it was part of the seatbelt interlock deal that never worked well and was discontinued. And probably a good number of 74s have been retrofitted to eliminate this little gem.