The most common reason for going the stand off box route is because you need somewhere for the powerhead to go when the motor is tilted up.
If you decide to go that route, be aware that your transom will only be 2" thick where the gimble was located, so you'll not only need to fill the hole, but strengthen the transom as well. I'd normally go with full height knees, bonded and mechanically tied into the engine/box mount bolts as well. 2 lengths of ally angle (12mm thick) is sufficient for that.
It is better to remain silent and be thought a fool, than to speak and remove all doubt!