"Ask not who toils for thou, engine bells, Darren toils for thee."
Or something like that
Looking good! There's no better way (to me, anyway) to make crude mock-ups to visualize where you're going, a nice visual/dimensional link between brain and build.
I was looking at you pictures, not envying you the task of making parallel grooves on the bells, but then it occurred to me that it's in my future, too!
Luck to us both! (tho' I suspect you'll find a clever way of doing it!)