I'm in the middle of a similar conversion now on a Zodiac Hurricane 733 with GRP hull, but using a proven transom bracket design from the manufacturer rather than doing anything innovative. This is my first time doing this, and actually undertaking it because I was curious about the process and also wanted to do some other modifications to the 733 I've been thinking about for a while. So I don't think I can offer any original wisdom, but am sure there are many others on the forum with extensive experience and definately more depth in regard to the the engineering issues. I assume you're consulting Ambar for their input, and would also suggest bringing the question to those on the Boat Design Forum (http://boatdesign.net)...there
are probably many other similar resources but I've found these members to be both knowledgeable and helpful with many questions I've posted.
However, I live relatively near you in Iowa and also was a paramedic for many years so can relate to your situation intimately..will be glad to help if I can. best of luck with the project.