Hi Roger H. After giving a little study of the metal and manufacturing technology in use during the years of Scott production, I came to the general conclusion that there was no great advances made between WW1 and the 1950’s. The manufacturing methods used by Scotts as described in the “Automobile Engineer” in Jan 1916 were still current until the late 50’s. As regards metal, then up to 1939, there were no national standards. It was only the war that obliged the government to impose a series of standard specifications on the fragmented steel industry. What we got was the “Emergency Number” (EN) series that is still very common currency here and even more so in India today. Those specifications were a compilation of common 1930’s steel specifications when a host of small steel companies made to different recipes. If the original Scott drawings from the 1920’s, 1930’s and 1940’s are studied, then the metal specification for loaded and hardened parts are just given as “3% Nickel” or 5% Nickel for example. We can see a parallel to the EN series 33, 36, 39. There is no supplier company or product name given. I think it fair to assume that Scotts bought quality steel from small producers that they trusted. Flywheels were bought in as stampings but no steel spec was recorded. I cannot say that I have ever seen a failure which was due to inadequate metal on a Scott. If we think of long stroke cranks or early steering head stems, then the failures in these components was due to design error, as the loadings were more severe than even the best metals of the period would sustain over an extended period.
If we were making the same components today, we could use steel with a similar nickel content to those specified by Scott, but we would have information on the other ingredients also.
A rambling answer perhaps, but given the lack of definitive information, an overall impression is all that can be given.