What would identify a Brookville 1931 Roadster Body

[37 Coupe]

If a seller did not know what he had or in a case I saw an estate auctioneer? What would be a quick dead give away? Gas tank? Do they use a different tank or you have to use an original? I don't think they sell any gas tanks as parts . Just something I was thinking about as I do know a local '31 roadster for sale and it is what is going to be seen more frequently an inheritance and a person who knows nothing about the cars restoration. I have posted about two others last spring that were local cars and I was told they were both Brookville roadsters on sedan chassis. At the time I never thought to ask or look at what would be different. They were both beautifull cars that sold very well.