Thanks for the great discussion guys. I wrecked-out the weedeater (man, did that feel good!) and found it must be the smaller size as the muffler has spring retainers.

Seems like the fins (backwards facing) could be reduced a little. Anybody got a favorite technique for rebalancing the flywheel?

And, something I've wondered about is just how necessary all that cooling fin area is. Am thinking of rounding-off the corners. Also, wondering if the project warrants installing a coupled ignition system???