ProForth for the Apple is fully FigForth compliant as well as '79 Forth compliant and should work on any 6502 with minor changes. With an Apple II emulator, you might be able to transfer the binary over to a .64 disk image. I can read and write to .64 image on my end, if that helps.
Or if you would ...

I am looking for an original Fig Forth 6502 Source File adapted for the C64.There are some Fig Forth systems without sources and of course Forth systems with sources (Durex, HES Forth, ... https://commodore.software/downloads/category/188-forth) unfortunately they are not as close to the Fig Forth ...

Maybe someone is interested. I ported FigForth to Michal Kowalski's 6502 IDE and emulator (http://www.exifpro.com/utils.html).
Have fun!
--Dietmar