Hi Michael,

This is the part I'm not sure about. It would seem that the distance along curve would only give you so much accuracy when the array is aligned
to a surface. However, the area of the stone (that needs to be spaced correctly) which is most critical is the "girdle" which is the widest circumference
where the top and bottom facets meet on the sides. So if a circle was grouped to the stone there, that might do the trick.. So if it was the closest points on circles grouped to the stone, that might work. In Rhino I remember grouping a point that was placed at the right level inside the stone to line things up for an array, so that might be another option.

As for prong placement that's going to be a tough one because when the curvature of the path curve changes, so does the spacing. I do it manually, creating some 3d scaffolding by offsetting curves and finding intersections and then copying and pasting circles to mid-points of lines I've drawn.
In this example, you'd need to change the diameter of the prongs just a little, making them smaller or larger or move them in or out a tiny bit, where ever the bend in the curve bows out or curves in more radically, so they (the prongs) cover the stone properly, so it's never an exact science. You kinda do whatever works while trying to fool the eye into thinking it's more uniform than it really is.

Jesse