I assembled everything except the weight and the petals, and found that the main assembly tilts to the left, as the weight is partially supported by the lower large gear resting on its roller and their is some slack in all the parts through which the drive rod passes. Inspection of the plans shows I omitted to include a brass bushing tube around the rod where it intersects with the main frame. It's possible that this fix will correct the lean, but there is also some space between the entire main assembly and the support frames.
In the interim, I want to measure the needed counterweight.

Rather than a jar with BBs, a gallon jug with water is used. Water weighs 8.3 lbs/gallon, so a half gallon (about what I have here) would be around 4 pounds. The gearing all runs quite smoothing turning the shaft by hand using its gear. I'll repeat after the leaning is corrected.