Ahh, I've had a few boats with the old Merc 115 outboard. Miss that thing, however, after rebuilding a few, it is the stupidest connecting rod journal bolt arrangement ever, you have to assemble the pistons on the crank, compress the rings of all 6 cylinders (requiring special tools) and insert all 6 cylinders into the jugs at one time.
I figured out a way to do it using hose clamps instead of the special tools... But what a pain.
Talk about a torquey motor, used to pull 3 slalom skiers out at once behind my old 1972 starcraft with that motor.
Your maxum control probably has the trim buttons on the throttle, which the original did not, and also that motor requires a choke switch, which your maxum control probably doesn't have.
I sincerely doubt an adapter exists. You're in custom world!