Seems several B4 riders are using Honda R/R's
I'm one of them.
I have a Cb400 RR in my b4 right now. The dealer had it in stock for $145 cdn. A little better than the $295 that the Suzuki dealer wanted, and a week's wait time.
No problems whatsoever so far with it, and it's been on the bike for months now.
Now if I could just get the bike to start.