A quick few comparison pics, the pinion shaft is a lot shorter, you can see in the last pic if I were to try and get the motor gear pinion more inline with the spur gear then the pinion screw wont screw down on the shafts flat edge so that's as good as it gets.
A quick 15 minute run and the motors barely warm, seems to have a bit more torque, wheelies a bit easier, Ill give it a better run out tomorrow and update but so far seems like a good replacement.