I am thinking doing something with the ball centers and the true angle for the slanted surfaces, intersections and whatnot.
I think I know what to do, but not how to do it. Trigonometry.
I didn't saw the real problem, so my first answer is zero !
I would mesasure a line on each side (or a plane), then create a generic line parallel to them at 4 mm, and create the intersect point, and a mid line.
I would measure the angle, calculate the tangent and calculate L.
Then I would create generic circles at the right distance (maybe by creating a local alignment to be simple).
