Rebuild stock shock? kinda waste of time, it's an emulsion type (no reservoir) and I don't see the plug for nitrogen fill, so that probably has to be added, loads of work and no gain.

Been doing some looking and '02-'06 CB900F (we call them 919 in US) has same length and mounts, but the spring rate from Ohlins is 1028 lb on CB vs 742 lbs on MC21. If the linkage system is same/similar on MC21 and MC18 I can order the 919 shock re-sprung and re-valved for 742 lbs. Ditch hydraulic pre-load adjuster and save few bucks as well.