Thanks again, everyone, for the feedback. Since the spoke cut-outs work so well, I decided to go ahead and finish out the flywheel.
Here's the steel pipe I used to make the rim. I sliced off 3/8" and trued up the bore, faces, and outside. I put the aluminum center in the freezer and heated up the steel rim on the gas stove. I left the aluminum OD about .006" larger than the ID of the steel rim. Once the rim was hot, the aluminum center dropped right in.
I re-ran the aluminum center thru my CNC program with a larger end mill to thin the spokes some. They are now about 3/16" thick and 3/16" wide.
CNC was only used to cutout the spokes and the center hole. All the other sizing and finish work was done on the lathe (baby steps...). I guess there is now another engine in my future. Can't let that flywheel go to waste.
Chuck