73 Plymouth duster gas cap and filler neck

I picked up a couple different necks and caps from a guy local to me one from a space saver duster and one from a swinger. Like a dumb@$$ I forgot to bring my old rusty one. Well the one was too short and was a 4 hole mounting flange. The other one was the wrong angle and neither cap would work on my old filler neck. The mounting holes can be welded in and drilled to match mine, but too short is too short. Even if by only a couple inches. Are the ones you guys have 3 hole or 4 hole mounting. What is the length? I'm fairly sure that I need one from a 73 duster. Thanks.