outboard Motor Mount
I think I recall that the transom of the Oday Mariner is designed to directly accept the OB. My brother had one many years ago and can''t remember for sure.
I would prefer a direct mount without a bracket if you can be sure of getting prop in the water. Also, check that the rudder will clear the OB - lock to lock. A direct mount gets you closer to the vessel centerline, thus reducing the tendency to cavitate in chop. Also, it puts less flexure in the transom than a bracket mount.
Also, check to see that everything works, rudder, mainsheet, etc, when the motor is in the up position and the foot clears completely out of the water.
Although, installing a bracket requires few mechanical talents, choosing the bracket and assuring yourself the transom mounting point is sufficiently stout requires some research and expertise. Checking out other Mariners might be advisable.
Congratulations and have fun.