[JesseK]

Wood is also easier on the tooling side of things too. Wood tools are less expensive, more common, and (usually) aren't so easily worn down like Aluminum.

For a flywheel, you don't have to attach the weight to the shooter wheel itself. So long as the flywheel is attached coaxial to the same live axle as the shooter wheel, you can use whatever material you want. Just be sure it's balanced or else it's rip itself apart at high RPM's. A good hardwood, 1/2-3/4" thick, and some 3/8" bolts might do the trick.