As many on this site are already aware, I ride and race my bikes pretty hard. We race local, regional, and National events, all in the expert or pro class if offered. As a result, our bikes take quite a beating.
Two years ago, my oldest son accepted support with a free bike, parts, work, gear, race money, travel money, etc. from a large Honda dealer. We had never ridden Honda's, and he was actually competing in the Pro class and Open Expert on a KX500. In order to keep his number 1 plate, we had his CR250 converted to a CR265 by Rick Petereson Motorsports (
http://www.rpmsbigbore.com/repair.htm). What great work! They actually did the work on a spare cylinder, and just swapped for our new cylinder, so turn around time was less than 7 days. We also never had one lick of problem with the Honda (except the suspension was never as good as the KX500, as Acme does not work on Honda'a).
For my current 2002 KX500, I actually have two cylinders. I swap at the end of each year, and have the spare inspected and plated by RPM. Also, if I am not mistaken, they do a lot of work for the factory teams.
Highly recommended. Check out the web page. I don't think you would be disappointed.
Rick