Posts are now coming thick and fast (relatively ;)).
After investing in some stainless steel hex bar and a few drill bits, taps, grub screws etc. I now have a motor shaft extension (courtesy of my lathe) which means I won't have to drill my new motor shafts when I make up the rest of the thrusters for my planned ROV.
Here's a clearer picture of it outside the tank.
The added benefit, as I've just found out in the tank is more thrust too, due to better water flow (presumably) around the propeller. Here's a picture of the thrust measurement.
I'm now having to weigh down my test jig as it now lifts up due to the increased thrust! I saw 1.4kg on the fishing scale at one point, divided by 2 to give around 700g, and the recircualtion of the water in there detracting from the true thrust should put it up near 1kg ....... hopefully.
Just the propeller shroud to try next (although I'm not sure how I'm going to mount it) and maybe fill it with oil too as this increased the thrust before, probably due to lubrication of the shaft seal.
Exciting stuff ....... for the ROV geeks among us :)