There is a used recirculating heater on E-Bay, its complete and has the piece you are looking for. Not "cheap" but is priced right based on my experience.

https://www.ebay.com/itm/254161086353?hash=item3b2d2e6791:g:pswAAOSwRfRch8hW

I've purchased two used units and still ended up having to buy a new round heater core. Those only became available in the last couple of years.

Good luck

Ron - - Dusty53
1954 Chevy 3604
In the Gallery Forum
"You can't dance with the Devil and then wonder why you're still in Hell."
"They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel."