ffbo? would anyone join a for f-bodies only

But they're not. There's overlap in engines and transmissions and rear axles and some brake parts, but that's it.

Looks like the forum at www.dippy.org welcomes F and J bodies as well as Ms.

They're not related in actual platform, which is what you mean, but I'd certainly say they are in spirit! When did the A-body end? When did the F-body begin? What physically similar attributes do they have? That sort of thing. Sure, in that sense, you could say that some other manufacturer's car platform is related, but seeing it from within the Chrysler ecosystem, I'd say it was a transition from A to F.