Technical drawings are the key. Almost nothing is available without creating it yourself; even WW1 Aero has almost nothing. If you look at the Stairs footnotes, the info came from Engel and DSA. I hope the estate of DSA keeps selling his work, I know he had 6 pages of drawings, not blueprint type drawings but details and dimensions. The details are the tough part. Drafting up from a 3 view is not to bad, but if you want accuracy you need dimensions plotted. You dont know what distortions the picture of the original 3 view has built in much less the blowup.