A little info here
JOHN "JACK" LEHTI (1912-1991)
https://www.pulpartists.com/Lehti.html
['He also assisted on the syndicated newspaper comic strip "Secret Agent X-9."
In 1940 he drew "The Crimson Avenger," "Sgt. O'Malley of the Red Coat Patrol," and "Cotton Carver" for DC Comics.']
John Lethti drew TARZAN from November 1948 to Feb 1949.
https://www.pulpartists.com/Bio%20Materials/Lehti/JohnLehti-Tarzan.jpg
[He also drew "Lassie," "Flash Gordon" and "Tom Corbet, Space Cadet" for Western Publishing.]
[In 1972 he drew "The Losers" and "Sgt. Rock" for DC Comics.] Not a bad record for a relatively unknown artist.
Cheers.
Link to the book:
Tommy of the Big Top 12 (alt)