From memory, the top bezel is curved on the 71/72 fenders to let the mast point straight up.

That bezel should be your solution, I think everything else would be the same. Here's an auction for one and you can see how one side is lower than the other.

http://www.ebay.com/itm/Mopar-71-72-73-Roadrunner-GTX-Satellite-Antenna-Bezel-/171022684193

Mike.