71 demon gas cap and dash pad?

I think I have an entire filler tube with the one vent tube which is clipped under brackets running down the tube. It also has the correct fitting painted fuel cap. I bought it by mistake and paid big bucks for it. I placed it next to my original 72 Demon filler tube and the first thing I noticed is that my 72 filler tube seems to be about 5" longer than the 71 filler tube. I also noticed that the cap on the 71 filler tube will not fit the neck of my 72 filler tube. So there are differences. I am in need of a 72 Cap to fit my tube. I also noticed that the screw holes on my 72 filler tube are only three and the 71 appears to have 5? I was just going to weld an overflow tube on my 72 tube and run it below the floor pan. I think on a 72 car, the gas tank had an extra vent. On the 71 car they used the tube through the floor next to the filler tube.