I did a rebuild with new materials now that I knew what I wanted. Under the handlebars:




I added sides on general principle.

the four hooks here are all that holds it on, and the center portion of the bar (hanging on the white bar there) is angled back to nestle under the stem. It's a lot more stable and solid than it sounds

Thanks for the help and ideas.

BTW it weighs 8.4 ounces (238 grams) which isn't great but less than I'd feared it would. I may wind up cutting the sides down since they aren't strictly necessary.