We did a similar upgrade on our 1987 Mac25 (Moonshadow).
The Yamaha was about 20 pounds heavier so we found a bigger bracket, one that had a bolt-in-place "pocket" for holding the articulating arm. This spread the load nicely on the Mac transom and made it easy to reinforce.
We added a small block and tackle lift from the outboard to the rear pulpit to make it easier to lift her up when sailing.
We added a remote throttle/shifter kit and a modified tiller (sledgehammer handle) for ease of steering in close quarters.
This has proven to be a great combo, quiet, little vibration, no burned 2-cycle oil smell when motoring downwind, etc.
We have the electric start with 14-amp alternator so the batteries are always charged.
Enjoy, Don & Betty on JCat or Moonshadow