Outboard mounted on swim platform

[Watertender3C]

I have a 9.9 Evinrude w/ a shaft extension, 9" I think, that I would like to mount on the swim platform of my 23" runabout to permit running at trolling speeds and traversing the NYS canal system, where the speed limit is generally 5 mph. Would appriciate ideas, comments, and suggestions.
Thank you

[Donn]

I've never seen a swim platform mounted strongly enough to support a 9.9HP outboard. Why not install a half-transom swim platform, and a proper outboard bracket on the other half of the transom?