Wood masts are a bit out of my area of experience...but I do know that if you move the boom to the main beam that you will loose the forward pressure that rotates the mast. You will need to have some sort of positive rotation device (which can be tricky and lead to additional failure if not adjusted properly while tacking). I would think it better to adjust the vertical angle of the mainsheet to control the amount of compression applied to the boom...imagine if you will, if your mainsheet were perfectly vertical, there would be no more compression on the boom and very little induced loading on the mast (although you have the same lack of rotation problem as with a beam mounted boom). There is a happy medium where the mainsheet induces just enough forward pressure to ensure proper mast rotation and you can achieve this by either relocating your traveler or the point at which the mainsheet attaches to the boom.