I did it pretty similar to the way Jim described it - I took a very fine carbide cutter and cut the blades off at their roots. I made a temporary contraption which allowed me to spin it on a prop balancer to ensure I had it mounted straight, and to check for balance while I spun it as fast as I could by hand.

I figured since I would use it in a non-cowled configuration, I didn't need the flywheel thrashing the air away from the cooling fins, and it saved a bit more weight. My 25cc Poulan weighed EXACTLY 3 Lbs with flywheel, prop adapter, prop, and engine mount. I never finished the muffler prior to the crash.