Yes there was the option of three motors in the original 63' MY. To my knowledge there were only 6 of this boat built that year and only one was a triple screw. All the rest were twin screw. This is not a planing hull in real life.
However you can get enought power in the model to get it to plane with no problem. As for the angle of the shafts I would set them in place with the struts and then mount the motors to that angle whatever it turns out to be. The props are counter rotating so there isn't the torque problem like you would have with a single screw.
Just get to work building the darned thing will ya?
And don't forget the pictures. Pete