Like so many Mercury things, there was a change at some point in time; so the handles can be found to operate either way. Earlier ones had the handle horizontal, with up being forward and down being reverse. Later ones had the handle vertical in neutral, with the more intuitive forward movement being forward and back being reverse. This change was made easily, because all they had to do was flip the shift cam in the lower unit over, so instead of facing to port, it faced to starboard or vs versa, I forget. If your engine would shift into forward if a vertical handle was moved aft, then your handle should be positioned horizontally in neutral.
Long live American manufacturing!
