filler neck gromet
Layson's lists it as part # DD-A0710 for $32.
While we're on the subject, I havent found the gasket for the top end of the fill tube at the quarter panel, also for a '70 Dart. Or the one on the trunk floor under the base of that fuel evap control pipe whatchamacallit that at least the CA cars have...
I guess I can pretty easily cut these out myself if I can't find them.