Actually there are four different head spacings and I recall 600,000 as being closer to the numbers made. A replacable and in Swiss competion legal elevation slide with windage is available. Check around SwissRifles.com some. Guisan may help with the slide. W-F made both drill and tap and clamp on types diopters. Pierre's excellent quality Swiss Products diopter(through Brownells and Grafs only) is a little less money than the W-F. Don't expect any thing to be cheap. Unmarked bolts are most common. It is considered a 0 bolt. Then there bolts marked as 5, 10, or 15.Best
PS Unissued or new is quite rare.