All been done before (like most things).
Go find yourself a H500 blade and all will be revealed.
Two holes drilled and tapped in the end of the spar. One large diameter and one smaller diameter toward the leading edge.
Insert threaded Monel metal plugs of length to suit. Monel = 8.4-8.8 g/cm3.
The size of these weights vary considerably on MD500 blades depending on the size of the "taco shells" fitted.
In the pic under the blue tape. You may have to zoom on the image as it is the best I could find.
