Challenger gas cap on 74 Duster help!

Danco said

72 BLU your answer is pretty much what I suspected I would have to do, So now I think I will try to get the gas cap area sheet metal from a challenger quarter panel and go from there. I also suspect I will need the fill tube from the challenger also and somehow join the that fill tube with the duster fill tube.
Of coarse this is based on assumption but I should be able to pick these 2 pieces used and at a fair price.
thanks

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Just out of curiosity I checked the caps and filler necks on my '72 Challenger and my '74 Duster, as well as one from a '74 Dart. The same locking cap actually fits all of the filler necks, but, the way the fillers mount to the quarter is different. The dart filler neck uses a flat mounting flange, where the challenger uses a mounting flange that's recessed. The result is a different depth to where the cap sits on the filler compared to the quarter. That's what lets the flip top arrangement work on the Challenger, the actual cap is recessed into the quarter and the flip top covers it . But since the Challenger cap you want is the non-flip cap, which is set to be flush with the quarter, you have to replicate that recess. So, what you would need to do is weld the end of a challenger fill tube onto your Duster's fill tube. The good new is, the fill tubes are the same diameter (as long as you don't cut in the middle of a bend, they aren't mandrel bent). And of course the recess in the quarter has to be from the Challenger.

I'm doing something similar on my Duster, I have a cap, quarter recess and fill tube from a modern Challenger to put a modern Challenger flip cap on my Duster. They're recessed into the quarter, unlike the original flip caps that stick out.