luckily it was not expensive, the one I ordered from Muscle Car Technologies I think the place is called. It is round. What I see that's coming apart on my Fury has a square flange. It will be easy enough to tell if the one I bought is the right size. Meanwhile I don't fill the tank too much so I don't have gas dripping (!) and so in case the tank has to be wrestled it won't be so heavy.
I really like my Fury, after you own it for some time, it doesn't feel like such a huge car. I loved my '67 but I like this '71 more and more. It drives easy and handles well. I never see another around here. The main things I don't like are the design of the cowl and firewall, the window mechanisms, and when you shut the doors you get a cheap sound. But still you can't complain too much, not many 47 year old cars are still around.