Don,

When I had Stig Pettersson redo my shock, he put a 12.5kg Hyperpro spring on it. Stocker was bottoming too much with my 160 pounds. New spring works well - still cushy but no bottoming, at least at my modest speeds. Hyperpro has a website that (amazingly) indicates an application for the MC21 (shock kit # SP-HO02-SSB003) - you might shoot them an email with your weight info etc. and see what they recommend. Hope that helps.
-Jim
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-Jim
'93 MC21