Here’s an article that mentions the diet of the first Mr. Olympia, 1965, Larry Scott.
http://www.rippeder.com/content/how-larry-scott-trained-and-diet
His coach bodybuilder Vince Gironda was an early proponent of low carb dieting stating “one burns fat in the absence of carbohydrates” in his book The Wild Physique.
And yet so many claim you need carbs to build muscle.
Tom Platz mentioned in a somewhat recent interview that he only ate steak and eggs and introduced carbs for muscle fullness. He later went on to say he wished he stayed metabolically flexible.
Serge Nubret ate like 4kg of horse a day.
Keto is best for body building as far as getting very lean. Once I got to under 100 lbs in keto, I began weight training and doing refeeds once week to replenish my leptin levels and it helped me lose an additional 11 lbs of fat. After a carb refeed my muscles looked huge! I was able to spend hours in the gym on literally 3 grams of carbs a day. Almost unlimited energy, plus the muscle gain was nice.