Hold on. Merc Motors before around 1969-1970 used to have the Gearshift Lever close to Horizontal when in Neutral. Lifting it upward, provided Forward, pushing it down, provided Reverse. I guess if someone managed to get the Shift Lever mounted wrong, the Control would appear backward. Post a Pic of your motor, it will give me a better Idea of the year, and based on what you posted, I suspect it is older than a 73. Also a Serial # would be a Help
Edit: did you have the Gearcase apart? It might be possible to get the Shift Cam flipped, and that could result in the Shift pattern being backwards. If not, how long have you had this motor?