Originally Posted by The Tank

with the 128 spur gear you should be able to get a 21 on but just barley. check to seeif maybe you can rotate the motor to another mounting hloe in the can, that's what I did for my 3.5. if you want to run a 20 you might have to be a little creative with a dremel tool. Billy Fischer did that to his and it fit like a charm. you simply "extend" the adjustment hole a little further, but I would try the 21 first before you buzz your new ride.