I'm building a 62 Plymouth Valiant and fitted a tank from a VF Pacer, basicly a Dart in the US. It has a nice flat filler tube that fits in the floor. I used a 68/69 Barracuda recessed flip filler.
I coated 65BCODA's gas tank filler tube awhile back. The pictures are on my old computer (so they're gone forever) but maybe he has a few. It turned out all right -- it had a hole in the side that required metal filler.