Sorry but the biggest one I've done is a 62cc. I have a big 125cc from a chain saw that I haven't done yet. Don't remember the brand but it's not going to be an easy one because the engine is part of the whole saw body so it's going to take a lot of cutting. Husqvarna makes some pretty big chain saws that you might find an engine from. When I am thinking of a candidate for a conversion, I look for a parts "blow up" or diagram for the machine to see how it is made. Something that has the engine separate from the machine itself is a LOT easier than cutting the engine out of a complete machine and is often easier to mount on a plane too.

Good luck and let us know what you find,
AV8TOR