Ok I don't claim to know exactly what these guys did, but I have talked to some guys, one who knew Arnold and another that knew Sergio. From what I was told these guys did a lot of orals. Test wasn't used all that much or at all back in the 70's It was considered a dirty drug. Remember that steroids were still kinda knew and were looked upon as something that took that place of test without all the bad side effects.
Dbol, anavar, drol and some deca and Primo. Winny to a degree also. I think that doses were fairly high. I know Sergio liked dbol, deca and winny, no test. For his comeback in 1984 he added test and tren and he had a different look, one that I personally did not like. I don't think that Franco had gyno untill his comeback in 1981.
Diet was simple, they ate roughly 4 times daily and like Tim said protein was first priority then carbs and fat. It was simple eating of good food.
They spent hours in the gym and why not? it was their job basically. I personally don't believe in over training. Things today are made way too complicated and they certainly don't need to be. Personally this is fine by me. I know that it is nearly impossible to convince these guys today otherwise. Yes genetics play a part, but today you have many guys with bad genetics who turn pro simply because they force their body to gow thru extreme drug use.