Apparently from a post on reddit - actually about Konami guns, but board is almost identical (has a capacitor added) it is a IS485E (they have a built in amplifier and schmitt trigger circuit)
You have to bend the centre leg because it was pokes out the wrong way to match the holes on the board, but once you have done that (and mounted it so the top is 7mm from the board so it fits in the right place in the gun) it works perfectly!