I’m not sure if you’re aware of this but, .fds roms have a 64 byte header where as the .nes roms have a $10 byte header. Maybe this is why you weren’t able to properly calculate the pointers for Deep Dungeon?
EDIT: Disregard the above, Hiryuu. I didn’t actually READ the file through before I made this. After a little research I found the .fds does in fact use the normal $10 byte header. I believe the above file may be helpful if you have a .dka version of Deep Dungeon.