Correct on 73. I don't recall seeing it in any of the SOR catalogs, mostly the firetrucks and the 6 wheel Cruiser later on.
I do recall seeing it in Marv's museum in person though. Had to have been 1995ish.
Looky here!!!
Only pic so far on the O'l Innerwebs...
https://www.tracksidephoto.com/gallery-image/77-Mint-400-Trucks/G0000.0wbBmUr4SA/I0000q2JK9AUm7qg/C0000yiPcDsgDsew