I am currently trying to figure out how to retro-fit a transom support onto my 730. I have a pretty good idea how I am going to do it but I'll always listen to somone else who has a better idea or has actually done one.
My RIB has twin 200 Mercs and the Standard Radar Arch attached which gives some extra support for the behemoths strapped to the back. I know I may be overpowered "a-bit" but hey, no guts, no glory. And you might even see this RIB on Whale Wars next season...