I've been making some progress on my project - usually by doing things at least 4 times til I almost get it right. I have the inner flywheel with the stub shaft complete. I ended up welding a steel plate onto the ends of my .75" walled cylinder. I then bored some bearing pockets and pressed them in. I then turned the cylinder between centers (no stub shaft at this point), and took a finishing cut. It seemed to work well, I can spin it up to 2000 rpm with no vibration and almost no run-out. Not sure if it's proper form to use deadcenters on bearings, but it worked good.
Trouble started when I attached the stub shaft (originally used 82 Degree countersunk machine screws). Everything was running true, I cut the shoulder for the bearing to sit against, cut the micro-grooves for the belt, the snap ring, and everything was good. However, I didn't realize how important those countersunk pockets were. These were cut on the drill press, and I don't think my accuracy was as good as it should've been. When I removed the shaft from the cylinder, and then re-attached it again - good luck! Out by .006"! I closed up the countersunk holes, ruining my pretty bright finish, and used hexbolts. Now I can adjust the bit of wiggle room and everything runs true again.
I attached a picture of my outer aluminum drum as well. I'm really struggling here - it's about 20 inches long, and my lathe only has about 16" of travel. I had a really nice finish on the aluminum, but then had to swap the drum end for end in the steady rest. The result is a fine line trying to match up the finishing cut on one half, with the finishing cut on the other. I promptly ruined the finish with some fine sandpaper, trying to get rid of that line. I'd ask for solutions, but I suspect the answer is going to be "buy a bigger lathe" if you want to do bigger work.
This forum is great, thanks for all the ideas and problem solving tips I've found in other posts.
Rollie