I’m not positive but I believe Mercury views their motors from the rear instead of the front as is normally done. In other words, what the rest of the world would say is a CW rotating motor, Mercury would call it CCW rotation.
You’ll have to double check but I’m sure this was the issue I had a few years ago when I rebuilt twin 470’s and had to get the correct starters for them. Both motors ended up being standard rotation with one of the outdrives being reverse rotation.
