The Manning brothers appeared in Experimental Model (r. 1964), when Joe was 19, Jim, 22, and John, 25. The footage was likely shot in 1961, since John first posed for AMG at 19, in 1955.

Here is an extract from the film (silent), from the compilation Fantasy Factory 5 (r. 1992).

Photos from the shoot:

More on Adonismale:

John Manning  https://www.adonismale.com/gallery/album/9044-john-manning/

Jim Manning https://www.adonismale.com/gallery/album/53282-jim-manning/

Joe Manning https://www.adonismale.com/gallery/album/53281-joe-manning-amg/

Sources:

John's age is mentioned in Physique Pictorial, Vol. 17, No. 2-4, January 1969, pg. 35