Plan "B"
A cornerstone (pardon the eventual pun) of SolidWorks training is the term design intent, in other words your design should always be built with the end result in mind.
After having to wrestle the existing medium U type model in Max I decided to go back and redesign the model from scratch keeping the ultimate destination of the file in mind, I abandoned my usual design practices and focused on building the model as if I was using Max.
I also decided to abandon the poly hungry end caps I'd been toying with for a less ambitious, but yet still quite effective (IMO) lower poly count treatment.
Of course the true test of this technique will be when I import this new model into Max tonight, if successful though, I plan to utilise the same method on the small U and large C type revetments designs.