No ones knows when the barrel change came in by number. Honda sold bikes and when the bolts ran out, they went on to a new box. It would of been the same with the barrels.
Not uncommon to see the rounded type fitted to a K1 and not uncommon to see a K1 head that was fitted to a K2 at the factory 
But, the factory never fitted the round front to a K0.
Thanks Graham - I thought I'd PM'd you with my question above so as not to hijack this thread, but failed miserably!
But what you say makes perfect sense and not unlike what went on with Triumph (TR sports cars) - even the dealers were swapping parts over and nicking tool kits etc.
Cheers, Andrew
