Many thanks Ashley and Dave for your advice and suggestions.
You both confirm my own thoughts on the motor size, but I’m not sure what effect adding the torque ring would have on the 540. Having briefly looked at other motor manufacturers data, it appears the torque ring will roughly halve the rpm (ideal) and increase torque available enabling the motor to spin a larger prop.
The prop size is as supplied in the kit (I’ve replaced this with Brass), and interestingly Dave Metcalf says in the instructions that he fitted a pair of 545’s and the boat is described as ‘over scale speed’.
Using 6volts, that’s just me trying to use my surplus batteries, but happy to fit 12volt if more appropriate.
Your further thoughts are most welcome and if anyone else has built this kit I would be interested in your experience
Pete