My 73 Charger had the same valve on it. I believe the original ones were these (pictured). But due to cracking and general failures they were changed out for the one you have.
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Lineman,
I bought mine at Rockauto.com. It's the same that you have now. Mine works great on my 73 RR GTX.
I used needle nose pliers and bent a loop around the pin. I made it a press fit around the pin. It stays put.