Having seen this perforated clutch bell I could't resist to drill some holes in a spare clutch bell from stock.
Wasn't the hell of rocket science to measure, puncture, drill, smooth and sand it.
Material is soft steel, so it drills easily. Balancing was done afterwards with my wheel-balancing axle, but not that much of inbalancy.
After that on the lathe to check its roundness, but was under 0.3mm, nothing to worry about.
We will see in the future whether it's eating clutch shoes or behaves as it should and stays cooler.