I know I'm going to be the only person asking this, but, is there any chance of the game *not* trying to copy / update the ROM font? I use a custom ROM / font (Clairsys) on my +3 which makes some characters in the game unreadable.
No idea if this is a major change or not, but it's just 768 bytes somewhere (also no idea what the print routine looks like, but if it's updating chars from ROM on the fly, then obviously this change might be a bit more difficult) :-)