Don't know why I didn't think of SHG, I bought the excellent pusher tug from them for boat rescues, plus other accessories over the years. They may even directly replace the geared drives. Time for paper, pencil and calculator.
Thanks.

SHG model supplies do a range of drive belts that might suit your purpose.

Have a look in their catalogue ................ http://www.shgmodels.com/acatalog/

Yep, I have outrunners & inrunners in various other boats, mainly non scale semI fast. This is a Düsseldorf that for some reason had Graupner gear fitted. it's quite noisy. I'll try sound deadening material first. Don't want expense of going to twin Brushless with reverse.
Reply from Antics on line, they say its Google not deleating old info.

If all else fails ...... outrunner brushless motors are the reason that drives like these are in decline.

Because the rotating section of the motor is on the outer part the leverage thus torque of the motor is way higher than an inrunner or normal brushed motor.

I am no expert BUT its recognised by the flying fraternity that outrunners can swing quite large props the same should be true for a boat.

Yes as suggested by Haverlock. Waiting for email reply

Have you tried Antics On Line?

Shows their stock as 0. And MFA no longer make them. Looks like they haven't removed the add. I shall email to check though.
Thanks anyway.

dunno if its any help BUT

http://www.anticsonline.co.uk/2019_2_1344480.html

seems to be still listing them