A few things that are recognizable in Youngblood. He did the most muscular like Mike Christian and there's only so many who do that. Second he had a "flat" chest and a tiny bit of gyno or whatever, the kind of chest that never can get that 3D/dianabol Arnold or Lou swell. Third, he's got a sloppy, unhealthy looking kind of vascularity. Fourth, he has an older skin tone and you can also see at the top ab and lower abs near the navel that he had a certain ab vascularity and ab skin thinness which older guys with thinning skin get more. Plus, for a timeline, he's got the pre-cookie cutter, pre-whatever drugs which make them all look alike today, more the post-Yates'-2nd-Olympia-contest look where they all started weighing more. I "snapshotted" it in my mind as a whole but that's how I'd break it down if I were to think about it.
On the other hand, I couldn't definitively see any tattoos and I was uncertain what you meant in your Ironage clue. 
I still don't quite get how you guessed, lol.
I do see what you mean about Youngblood's "flat" chest, compared to Arnold and Lou. I know what you mean about the abs vascularity and skin quality of his midsection...but I'm surprised you even noticed that in this picture, as his front upper body is so covered up due to the nature of the pose - I see what you mean about the way that Youngblood hits this shot, but you would have to be quite the bodybuilding fan/historian - in addition to having a great eye for detail - to notice such a thing.
It's also worthy of note that the video I posted above where I took this screen capture from is the only video I have ever seen that has Youngblood talking. I had no idea how he even sounded before watching that video. I also had no idea that he looked that lean EVER, which is the product of GMV's high quality camera and good lighting to produce great footage, which I was then able to crop this screen capture from.
I had never seen Youngblood looking that hard and shredded before. Basically, his muscle density, which is unlike that which I have ever seen before, and that says a lot, because Youngblood always had great muscle density/hardness. Because I had never seen Youngblood look this hard before, I would not have guessed it was him - perhaps I would have recognized him if I noticed the arm tattoo - but I didn't even see that in the above picture, due to the lighting!
So the one most obvious clue you had...you didn't have! And yet you still guessed Don Youngblood, haha.
I'm seriously impressed. I don't really get how you did it, even after you just explained in great detail, LOL. Great work!
What can I say? I have always been impressed by Megalodons.
Don Youngblood, competing at the 2001 Mr. Olympia contest, where he placed 2nd to Vince Taylor. Don was 240-lb on the nose at this contest, at a height of 5'9.14":
