Challenger gas cap on 74 Duster help!

I really don't like the look of the duster gas cap and fit. I would like to fit and weld a 74 Challenger regular gas cap ( not the flip top one) I was wondering if any one here has done this and what I would need to do it. I am pretty sure I would need the piece of the challenger sheet metal from the quarter panel but would I need anything else other than the gas cap of coarse?
Any help including the piece of challenger quarter would help.
thanks