SE and SP bikes have the same cylinders.

'21 to '28 porting is different but not enough to really matter, as Honda say, the '21 barrel is deleted and the '28 one is the replacement for it.

Honda supply of new barrels is depleating and they will almOst certainly not be making any more so if you're insisting on new you're going to have to take what you can get, if there are no 'B' cylinders left then that's that unless someone has some in stock somewhere.

Bearing in mind you're on about a near £400 purchase just on the off chance you need it (a new SP barrel) you may as well just get the matching (£40) piston surely?
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