Re the lowered Merchantman floor, I've just found this Pprune Vanguard thread from 2009, entaxei's post #76. I does sound like a lot of work but it must have been worthwhile modification.
Vanguard
Quote:
I worked on the hangers for a number of years on production control, including on the Vanguard conversion, re Merchantman floor height - yes they were lowered to accommodate the size of the std containers then being used, we also had to modify the fuse structure to take the door frames and additional loading. Each conversion lasted some weeks, it was a full stripdown.