Different training?
Hard free weight training with some cable work and Smif Machine stuff along with genuine steroids and a real freakin' tan instead of that diarrhea in a bottle shit these "health conscious" ("OOOoooo...Too much sun exposure can cause skin cancer!") bloat babies use now produced physiques like Franco and Arnold.
I met Franco in '75. Fantastic physique and a great sense of humor. Strong but not an asshole about it at all. If he had an "attitude" it was one of just being happy to be alive. To me, the '70s was nearing the end of real bodybuilding. These guys got off the stuff when there was no need for it. Another great guy was Ken Waller.