It's slightly complicated I'm afraid:
first, fbn's nvram file (.fs) is compressed somehow. I'm not exactly sure how. On the other hand, if the nvram is a standard 93c46-style eeprom, its uncompressed as "romname.nv"
most 68k games have byte-swapped nvram in mame, but fbn is not byte swapped.
best regards,
- dink