If you drop the motor to the lowest posistion on either side, there is much less flex, and still no loss of space. Im back to running a normal-ish motor mount now, but I may have to work some more custom magic if my hacker clone is too fat to allow 24/62 gearing to mesh correctly...
Thanks for the advice - quite tempted to get somebody local to machine a stronger aluminium piece with the same design to stop the flex. I was also thinking of making a simple aluminium mount in the traditonal emax design with further away mounting locations ie 'mickey mouse ears' and using a large pinions..