BEEF, I have no idea if that photo was shopped or not but I can tell you this.....
I met Don a couple of times .... but the time I can best recall took place at the old Embassy Auditorium in Downtown Los Angeles sometime in the early to mid 1960's at one of the LA bodybuilding events.
Gene Mozee was on stage as the contest MC and Don came walking down the left side aisle wearing a blue cardigan sweater.
Nice sweater but what was most impressive were his deltoids which were massive and appeared to be bursting loose.
Once upon a time Gene had a gym in which Don trained so he acknowledged him while he was taking his seat and made some polite comment about his delts.
I had been around serious lifters of all types back then and had never seen a pair of deltoids that huge.
So I doubt that any of his photos with impressive delts have been shopped but it's most likely that his delts were somewhat smaller after he quit bodybuilding after the 1960 (but I could be wrong about the year in which that occurred).
For more interesting info such as his serious back injury and eventual recovery, his only (?) Hollywood movie and the role he played, HS gymnast, and his family ... go to IMDB and search for Don Howorth.
By the way .... he may be reading this. If so, please let us know if I am recalling this correctly.