I just finished building my 73 Bonnie into a Streettracker. The only thing I´d like to improve is the gearing in 5th. It´s running about 3,600 RPM at 60 mph, and I´d like it to be more like 2,500. There´s already a 21 tooth sprocket on the front, so I can´t go bigger enough to make the change I´d like. Is the 5th gear from later bikes any taller? Thanks, Jim