Hello Mark,I regret I haven't time for more than a brief reply at the moment. There are no surviving original plans (that I know of) for the Titanic collapsibles, though there are drawings of similar boats. The 1912 Wreck Commissioner's report gives the following dimensions that you may find helpful:
"4 Engelhardt collapsible boats, 27 ft. 5 in. long by 8 ft. broad by 3 ft. deep, with a cubic capacity of 376.6 cubic ft., constructed to carry 47 persons each."