Those are all extraordinary bodybuilders. I am talking about what applies to typical gym members, most are a lot taller and narrower than the ones you mentioned. Length of the arms will determine the effectiveness of the exercise choice in targeting the pecs.
It seems that the majority of bbers in the 70s had great pecs, and used barbells. This was noted in another thread about a year ago. A lot more could be listed than above. And as far as height, Arnold was what 6'2, Serge Nubret was 6'1, Sergio was 5'9, Lou at 6'4, Franco was 5'4-5'5, Robby was 5'7, Bertil was 5'10.
So, all of these guys had great chests and run the gammit of a 6'4 Lou to 5'4-5'5 Franco. Which dismisses your "a lot taller and and narrower" comment.
True, arm length does account, but there are other factors.