Re: is there a reason for using wood in the transom
I suppose you could do it, but there are some reasons that wood is preferred for most applications. Aluminum is light and strong, but it is not good at absorbing vibration and it fatigues and work hardens. There are some very expensive boats that still use wood in the transom simply because for it's combination of weight, strength, fatigue resistance and vibration absorbing abilities it is cost effective and it works.
In your situation, welding an aluminum plate in and then adding wood behind it would work very well.