The link to the HBSA article that Roger quoted from above is here:
http://www.hbsa-uk.org/knowledge-and-research/journal-summaries/hbsa-journal-volume-4-2009---2018

The article on the .375 Lee can be found in issue Vol. 4, No.10 (2018). The full article is 19 pages. The material is taken from part of the chapter on the .375 that will be part of the upcoming Lee Speed book. Since the article was published, a few more things have been learned on the matter, but they tended to affirm what was surmised. For example, further evidence has confirmed the theory that it was gunmaker C.W. Andrews who introduced the .375 model, though this was in 1905, not 1906 (off by one year!)

Back to the magazines... Hendo, thanks for the info about the magazine reproductions. I'm eager to see you or Darryl share some detailed photos when the .375 mag is done. Any plans to make more? I know several people who would be interested. Congrats on this project.

How about a repro 8x50 Lee Speed magazine? There is a definite need for a few of those among collectors.