I looked up part #s for 70-74 and came up with the following-
70 - 3441034
71 - 3441884
72 to 7/73 - 3502346
after 7/73 - 3502723
The first 3 #s if I'm not mistaken, are all variations of the red/black bakelite unit, and the last is the metal valve.
From what I've heard the bakelite unit was prone to leaking so it was replaced by the metal one.
So I think that's why we are sometimes seeing the metal valves on the earlier cars.
I took a metal valve off of a 70 318 Challenger back in the early 90s myself.
3502723-
https://www.ebay.com/p/1722984198https://www.ebay.com/p/1722984198?iid=3818922220263502346-
https://www.ebay.com/itm/NOS-MoPar-...2?hash=item21688c01b8:g:2VUAAOxyjP1R24iihttp://www.bradsnosmopar.com/cornosebunac.htmlIs it possible that the aftermarket started producing metal valves in 1970-71-72?
https://www.hiltopautoparts.com/pro...rol-valve-1970-3-e-body-1972-3-b-c-body/ 
