I just designed and had a machinist friend manufacture a custom floating jackshaft for my cb750 chop. I did it because it has two outside downtubes instead of a single like my xs650 so the left downtube was in the way running a fat back tire. Also I did it for the cool factor...lol. Anyway, one of the xs650 sites sells a nice jackshaft...
I haven't run mine yet as the bike is still in mock up, but it all came together nicely and I expect no problems....