The sticker on the board and chips will look different, from what I've seen anyways. You can take a Super C board and replace the Super C chips with a set of custom Ninja Gaiden III chips and there you go.
I'd prefer to have the original as it comes with the "tips and tricks" screen whereas the custom chips don't.
I just stumbled across this person's site and he may be able to help you find this PCB! Check it out. http://www.panthersplace.com/pc10/pc10_game_cartridges.htm
He is currently out of stock on this exact PCB but he is resourceful and more than likely can find it.