Modify FF2 to MMC1 is very easy, you have just to replace some "bit $fff9" for a "sta $fff9", (I've already tried this just for fun). Looks like this game was first design for an MMC1, not for an UNROM mapper.

I was under the impression that FF2 was MMC1 (same board as FF1), and the UNROM version was a mapper hack.