Well I have decided to give a small brushless motor a try.
I had the parts in the dockyard so it's worth a try.
I am going with a Turnigy 450 outrunner motor. It has 250 watt output but is about 1/2 the size of the brushed motor.
The 890 KV rating should get me to almost the prop speed of the Viper motor.
The motor has a 4 mm shaft so it was to big for the stock 1/8" coupler.
So I made a 4mm coupler on my lathe.
I was able to modifi a airplane type motor mount I had in my parts bin to mate the outrunner to the Neptune motor mount assembly.
The outrunner motors cool through the stator so the Neptunes mount being in the water on the outside will add some water cooling.
I should be able to do some current and temp tests next week. BD.