When getting interested in serious intent lifting (at 16), a friend of my uncles had a collection of original Iron Man magazines, dating back to the '50. I want to say late '40's but I might be wrong. He let me borrow them for a while to get some ideas about training. Bruce Randell was a feature in some of the articles. He gained most of that 400(?) while in the Navy, stationed at Great Lakes, if memory serves me right. Don't know why the Navy let him get so overweight, but that was the story. Must have looked great in a set of navy blues. Ready supply of food for him, most of the time. I've heard the Navy gets the best food in the service.
He did the old fashion heavy, high rep training mostly. With squats, Hise shrugs, Hopper DL's, SLDL's, Hip lifts, presses, etc. Not just 20 reps but up to 40, at times. That heavy breathing induced with moving outrageous work loads, with higher reps, almost demanded that the body get larger and stronger. And very fast at that. Probably had a lot to do with his impressive chest/rib box development. Compound exercise were king back in those days. That and drinking enough whole milk to float a boat. Some guy's drank half & half than. Of course meat and eggs to round out that well balanced diet. Randell, and guy's like him, didn't want to look pretty, just slap on the muscle. Adding extra fat was not the main concern. That would be the concern after gaining the muscle mass while hoisting huge training weights.
I believe Randell was doing inspirational speaking tours at high schools last I heard. He must be in his 70's by now. Good Luck
Side Bar:To the older BB'ing vet's; In that photo of Randell with the two other gentlemen, is the one on the left Bob Hinds? I believe that's his name. One of the truly natural muscular men of that era.