Challenger gas cap on 74 Duster help!

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