Morning All
@Tony, I didn't know that the Aquaramas were sometimes rebuilt with diesels, part of the ownership would be the throbbing V8 sound I'd have thought..! But I think marine gearboxes are always reduction ratios aimed at slowing the shaft. To be honest I've not looked into that for the full sized boat.
@Derek, interesting points raised. I'm not assuming any thrust bearings in the motors as far as my use is concerned. Having said that I guess in their aero role the motors do have to take the full lifting force on their shafts so must have some capability...
The standard mount is the 'X' plate:

I intend to create a similar 'spreader' solution from aluminium plate, and incorporate water cooling channels.
My current thought is then to use some 7mm walled Aluminium channel (I use this in other work) with the motor mounted via 4 bobbins on one end, and the prop tube rigidly mounted at the other end (black pen in pic below). And a solid coupling in between, the motors have a 6mm shaft, and I'd use 6mm prop shafts. The base of the channel then becomes the mounting surface to the hull.
The bobbin mounts will have 'cups' of either aluminium or nylon around them to reduce torque induced movement, so they just eliminate solid mounting to the hull, but don't allow the motors to move. In this kind of arrangement:

I may look at not having a prop tube top bearing, just a seal... Using the motor as the top bearing with a solid coupling, so they don't fight each other... (There's a thread on this in R&D section.)
This then gives two options for taking the thrust.
A suitably mounted / integrated P bracket, or the motor mount (left side in pic above) using a more conventional thrust bearing.
In terms of the potentially brutal power of these motors, I agree it could get catastrophic... I'm planning to use the 80A Neuron ESCs from FrSky, these can be programmed to deliver super smooth acceleration, even if the users stick input is less than smooth. I'm using the 40A versions on my 1/10th and have arrived at very smooth low speed handling and acceleration.
The Translock system looks very elegant, more so than the usual collars with a grub screw, thanks for the link. I'll try to find some and report back.
Thanks for comments, and best regards to all.
David.