It is possible but you only gain around 500 revs per gear.From what I recall it also requires the 650 clutch or part of it.I personally don't think the mod is worth it.
It's common when you get these bike you think they rev too high but they were an innovation at the time in many ways.They one of if not the highest revving push-rod engine made and were designed to handle the revs.I can cruise at 70/80 all day and they love it,even giving a good fuel return of well over 55+ UK miles to the gallon.
Join Chopper Charles site as well,
http://choppercharles.com/cs/forums/There's a lot more traffic on there and a good Customization section where to ask.Bear in mind they are only a 500cc engine and if I were doing a lot of really long mileage I would go for a large cruiser like a Honda ST1100/1300 or a Sports Cruiser like a Bandit or FJR but for the UK and most roads the CX is a bargain even if you have to do some work on them to bring hem back to good condition.
For town and country they are excellent and city hopping IMHO plus of course the owner can do well over 90% of the work on them at home with minimal tools not to mention the conversations you get
