Thanks for all the comments!
About the unofficial opcodes, and as already mentioned, they run just fine on real hardware, so I'd say any emulator that has a problem with them is broken. Our main concern was making it run fine on a real NES, both PAL and NTSC.
The game works fine in Nestopia, FCEUX and Nintendulator.
And about flag 9 in the iNES-header, as thefox already pointed out, it sets that it's a PAL game. Most emulators just ignore this, but it seems to work as it should in Nestopia atleast. If you'd like to play it in NTSC speed you can just choose NTSC in the emulator.
tepples wrote:From the manual:
It looks like you don't want people selling reproduction cartridges of this.
If someone would want to make a reproduction cartridge, just contact us and I'm sure we will be easy to deal with.