I am somewhat familiar with these Craftsman propane trimmers. They are built by Lehr, a company that has a line of propane powered lawn equipment products. The engine on the trimmer you are considering has a Chinese built version of the Japan built Subaru Robin EH025 with a propane carburetor system.

The Subaru Robin EH025 does have conversion potential, and is the base engine for the The Fuji Imvac BF-25EI

http://www3.towerhobbies.com/cgi-bin...?&I=LXJDJ5&P=7

I do not know if these Lehr engines are any different internally from the EH025 as far as compression, or ignition or valve timing though.

If you decide to pick up the trimmer and chuck the propane system parts, I'd like to buy those parts to use on a motorized bicycle project I am working on.