No problem fitting an MC28 SE/SP head to an MC21 SE/SP barrel, or vice versa. (Also, no problem interchanging R heads between 21R and 28R, just don't mix R and SE/SP unless you know why you are doing it!)

One of the studs in the barrel will be too short, so you will need to sort that too. Be careful extracting the stud, as it's easy to damage the barrel if it's in tight! Soaking the day before with penetrating oil may be a good idea, if it looks corroded. (Especially true when removing MC16 and MC18 studs, as the barrels are considerably weaker in that area to MC21/28.)

You will ALWAYS need to check the jetting with ANY modification. To not do so risks the possibility of detonation damage to the piston/head, at the very least, although this modification is aimed at reducing such chances in the first place. You should always be prepared to make carburetion changes.
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Andy.
NSR-WORLD.COM

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