Chris Willis came out with a book awhile ago called the NFL 60 Minute Men: All Time Greats of the Two Way Player Era, 1920-1945 in case you don’t know Chris Willis is the head archivist at NFL Films and was a member of the Blue Ribbon Panel that elected the Centennial Class he’s written multiple books about Pro Football I got it and I loved it I recommend it I’ll put a link to it below
https://www.amazon.com/NFLs-60-Minute-M ... 1476691320