I also have a 36" boat that had the MFA 850 fitted. Acting on advice from Canabus I bought the Turnigy 3648 1450kv from Hobbyking UK. I had heard that Hobbyking can be a bit slow to deliver but it was there two days later. For an ESC I ended up with a Leopard Hobby (HobbyWing) 120a waterproof type that is designed for rock crawlers. 120a might be overkill but it is reassuringly solidly built and has a bigger fan than its (brushed) predecessor, I used Canabus' settings to programme the ESC with the program card, but mine has the option of forward/reverse without 2 taps on the stick. The ESC came from The Component Shop, ordered at 15.30, delivered next day at 14.00, pretty impressive.
Two couplings, one heavy duty rubber, one solid (used for setup) came from Model Boat Bits and Steve was kind enough to include a short length of 5mm shaft at no charge. 42mm 2 blade plastic prop from Cornwall Model Boats, but I will try a smaller prop and compare performance and, hopefully fit an alloy type once I am happy with the result.
I also chose to fit an aircraft type motor mount (Great Planes, medium) the medium size mount needed some filing and drilling to fit the motor but is a perfect fit in the engine room, the large size mount would fit the motor perfectly but take up more room than I have.
If all goes well the pudding will be proved on the lake on Sunday.