Just for information, I have now fitted the new motor mounts into my Bilsdale hull and the method of tensioning the drive belts works a treat. The mounts are glued in. The motors can be removed but it will be a fiddly job to refit so I will probably cover them in cling film while I finish off the hull.
The distance between the motors and the paddle shafts vary a bit due to the siting of the shaft and shape of the hull but the drive ratios are the same. For some, not immediately obvious, reason the forward motor with the longer drive belt gives 322rpm and 0.6amps at 7.2 volts whist the aft motor is delivering 334rpm at 0.5 amps. Both wheel shafts seem to be equally free running. It's difficult to get the tachometer on the motors themselves as the aluminium pulley is reflective. I may try masking it though.
By running the motor with a wattmeter in the circuit it is possible to monitor the current draw while moving it along the track to adjust the tension which in turn makes it very easy to identify the 'sweet spot' where the belt has maximum tension to avoid slipping without pushing up the current draw.
Just got to finish the rest of the boat now and assemble the feathering wheels.
Colin