I seriously doubt this is going to be of any interest to anyone here. Most balk at the idea of spending anything more than a few hundred doing a conversion, and never, just never on bikes that cost 4 or 5 thousand pounds.
Gearbox motor costing $2500+ just for the motor, then the costs of frame, etc etc and dare I say it.... etc.
So you're probably looking at bikes starting about the $8K mark.