any 8 NGK is two grades colder than the 6 you are running
If you do long rides they may be fine but on short rides thy will tend to carbon foul
They will also tend to do this on the over run going down long hills under engine breaking .
The 4 character number underneath is a stock number and of no consequence to you if you regap the plug ( which we all should do )
The same plug with different gaps set at the factory get a different number as does the same plug in blister packs and in factory 144 plug tray .
Plain B anything is being deleted in favour of
BP , projected electrode which is what I use
BPR / BRP which are both resistor plugs and should be avoided as they put a high load on the magneto .
As adviced, get some 6's from some where else
FWI I use 8's 7's & 6's for different times of the year & different types of use .