From what I remember you have the diff screw on the motor side... so if ur running mid motor and you look at the car from the front, the diff screw will be on the left hand side.... but if you're building it as rear motor then the diff screw will be on the right hand side.
The fact that you can use the diff in the same direction with the diff screw in either side, would suggest to me that it doesn't really matter which way round you put it.
I reckon they suggest you having the diff screw on the motor side in each configeration so that it is easier to get to when you wanna adjust it... clipping off ball studs on the spur gear / gear cover side is a always a pain in the backside as there's less room!
I'm sticking with the manual... no problems so far
