Filing the camera...that doesn't sound at all like it will end badly.

C&P from the Mir site - " The additional finder release lever activates a pair of claws which cinch the meter on to the body via the "Nikon" bodyplate. Older F's (serial numbers before 6900000) may need some filing to get the nameplate to accept the FTn properly."

This page - :

The nameplate is held on by two screws. Remove the nameplate and round off the bottom corners with a #5 or #6 file, reinstall.