Hi Stu,
I have just recently fixed the same issue, as far as I am aware the internals of the gear box are the same.
The chain gearing is different.
Side car: 18 front, 47/49 rear.
Normal: 18 front, 42 rear.
With the side car gearing, very quick off the lights and not alot top end.
Normal: a little clutch drag off the lights, but great top end.
For the speed nuts, go bigger on the front sprocket.
Oh, suprise suprise, Brian suggested exactly that
...........
I went out for a ride on the weekend up got upto 90 MPH on the normal gearing, next weekend I'm gunna have a crack at 100, armed with not much sense and a full sack of brown Adrenalin.