As they say speed kills.
Look, the muscle mass Lee had was not that great in modern day terms.
Most guys can achieve that level of muscle mass, even relative hard gainers.
You don't need anything fancy, just a good basic weights program and diet. He was training to do something else, you can just focus on the look.
Now the killer crunch. Say you build up the mass and you are fairly lean, the thing that really makes his 'look' is the definition, seperation vascularity etc achieved by low body fat and various 'tricks'.
And that's the bad news, you can't look like that ALL the time, it's peeking, look at lower weight division boxers at a weigh in, then see them even hours later.
Same with body builders. You can have a really good body, but to look like that all the time is not human.
Sure get yourself some speed or Clen or Iggy Pop Chase as opposed to enter the dragon. But leave the look for the film shoots if you want a healthy and long existence.