Other than that he was born in Pennsylvania and, like so many pulp era illustrators, studied in New York, I couldn’t find much information online about the artist Jerry Allison. (Most of the information I did find was about a different Jerry Allison, who was Buddy Holly’s drummer.) According to AskArt.com, Jerry Allison studied at the Woodstock School of the Arts Students League and, along with his work for the pulps, he also did illustrations for Reader’s Digest, General Electric, and NBC. After he retired from doing paperback covers, Allison concentrated on panting historical scene for the calendars put out by the Esso Corporation. (In the United States, Esso is now known as Exxon.) This is a case where the artist’s work will have to speak for itself.
Allison’s covers all contain the usual pulp elements of manly men, beautiful women, thirsty stares, and guns. One of the books below is called “The Lusty Men” and that’s a good way to describe most of the men who appear in Allison’s covers.
Considering that’s a fairly modern bra for a book that appears to take place in the Old West, there’s a chance that this final cover may not be historically accurate.