The artwork is not by the great Septimus E Scott. It's by the far less talented Philip Mendoza (first and last pages) and an unidentified other. Unfortunately, Scott never drew a Three Musketeers strip. (But he did paint the cover for TCL No81 "The New Adventures of the Three Musketeers".) The excellent cover for this issue was based on a still of Douglas Fairbanks in "The Iron Mask" (1929) and was painted by George Cattermole.(David Ashford & Steve Holland: "The Thriller Libraries" 2010)
Link to the book:
The King's Captain