Try to find one with the 78mm clutch. Some of the John Deere weedeaters used to use the Mitsubishi TLE43 two-stroke engine - don't know if they still do or not. A 78mm clutch is going to be used on a larger cc displacement though - at least 33cc. (Most of the smaller weedeaters engines are 20-25cc, and they use either the 54mm clutch, or an off-sized clutch.)
Staton sells his FD in the 54mm clutch as an option, but AFAIK, he's the only vendor who even offers anything other than the 78mm version.