What about this idea. You pull the bravo drive and bolt onto the gimble, a housing with drive shaft and dyno attached. So now you hook up the water and start the boat on the trailer and can DYNO the engine while it is still in the boat.

There is a company that already makes one. It goes on the prop shaft though. The name of the company is escaping me right now...but they are pretty popular for their drive stand off and the shifting props.

There was a board member that was also developing a real time on board dyno. There need to be a jackshaft or drive shaft that he would then measure the strain off of. It sound like a really neat system.

LAND AND SEA MAKES THESE NOW <<<EVEN FOR R/C MOTORS <JETSKIS

We have a K&O dyno that we use for some basic muffler testing.
They are even available as a Mercury service tool, good for about
550 HP. Not very accurate for engine development, but great for
repair work and not having to haul to the water for each possible
fix.

i have a land&sea dynomite propshaft dyno and the thing is great.

I had that idea! Pull the drive, mount to gimble and drive shaft into coupler. Mount the dyno on some kind of hoist for alignment. Actually sounds pretty simple.