For those unfamiliar with the boarding ladder design on the X and M macs, the ladder is a hinged affair attached to the transom of these boats. Due to the space requirements of the outboard engines, the ladder is no more than a foot wide. A swimmer is expected to climb up the narrow ladder and squeeze between the engine and the cut out on the transom. Although I have never boarded an x or M from the water, I have climbed onto both types on dry land, and I am slim and agile.
What kind of alternate is available? I have seen a boarding ladder that uses brackets with slots that the ladder is slid into, and then pulled vertically out of the slots when getting underway. This kind of bracketry will definitely need backing plates. I like my ladders to go at least one rung into the water when deployed as well. Think long and hard before you drill.