Please let us know if you purchase - good question. I'm not so happy with smoothness of the stock mainsheet ratchet. I've looked at the Harken catalog and it's tough to tell what would work. It looks like the airblock series can be dissembled, which would allow the metal post to be inserted in the whole in the bottom. I have not taken any measurements yet, but I really prefer the slide mechanism for the ratchet on the Harken.
In the catalog, there is a "double-line" mainsheet setup (not sure of the official name). It looks very cool; it effective gives you gross and fine control - pull both lines and the mainsheet moves in "high gear" or pull one line and the mainsheet moves in "low gear." Like all Harken - very pricey, but very cool. Cheers, Kevin.
Lived aboard 30' S-2 Center Cockpit for 13 years (Milwaukee WI / Corpus Cristi TX / Miami Beach FL) about 12 years ago. Don't miss the maintenance, but miss the sailing - Just purchased Used Hobie-Bravo - WOW!