The right side shifter / brake combo isn't as bad as it seems - in most cases, you're only going up or down a gear or at most, 2, once you get rolling and on the big bikes, a lot of times not at all.
My Can-a-Bul circa early '80's (CanAm motor, Bultaco Astro chassis) and current Starracer RM Suzuki have this setup and it works far better than you might imagine or maybe I just got used to it. Don't know if I'd want to try it on a street bike though.
As far as the CX500-turned-dirttracker, a bar story goes that an expert dirt track racer and his sponsor contacted Honda North America regarding getting a motor, the AMA rules then were you had to have 25 copies of the motor "readily available" for sale or some such (it used to be complete motorcycles not too many years before).
In 1982 dollars, the motors were 25K apiece, so... not (m)any takers.
As one wag put it, you'd be buying a million yards of heliarc welding if you got one. Do a google search and look closely at the photos - you'll see what I mean.
If you decide on such a build, keep us all posted. For sure, you won't see a clone of your ride too often.
Regards,
Pat Cowan,
Vintage Motorcycle Fiberglass