I think you are mistaken when you go to bike check its cylinders and exhaust its a twin piston bike not single piston if it is single Piston then it is not a SL350 and some other bike ..
here is wiki article which explain different flavours of CB350 as SL350 and CL350 :
The CB350 was also offered in scrambler form, as the CL350, with high-mounted exhausts and a 19-inch front wheel, and as the SL350, with upswept exhausts and off-road styling.
Ref# Honda CB350 - Wikipedia, the free encyclopedia
Some reference pics which show its both cylinders or Silencers:
hope it helps.