AFAIK, nobody makes conversion kits for Echos. But if you are reusing the magneto, all you have to find is a prop hub that fits the output shaft thread - probably 8M1.0 or 8M1.25. You can get one of those from several different places, including CH Ignition and I'm sure RCIGN.

Echos make great RC engines. Too bad they are typically pricey so not too many folks care to convert them.