WSB do not allow a change of crank for anything other than 1000cc twins. The cranks can be polished and balanced as well as surface treated but must remain as homologated. BSB have the same rule but pistons cannot be changed in BSB and must be as homologated. They may use another make but if they have an oil ring as stock then they have to have an oil ring in the ones being raced where WSB can use simple 2 ring pistons. Valve lift is limited to no more than stock in BSB but duration is open. These two differences doesn't make much difference in power but does mean the BSB bike will be less reliable at higher RPM and BSB bikes usually run lower rev limits due to the cams and the heavier pistons. SO the bikes will not seem to different if the BSB is allowed to rev higher but it will have more risk of failure.