Mike Tyson was a genetic freak. At 13 he weighed around 190 pounds with a bb physique. He became a heavyweight champion at the age of 20, weighing in at 220 pounds of solid muscle.
As far as I know he did not use weights for his training in his early career. He only did shrugs with dumbells and running with a backpack with weights (cause Cus did not want him to get taller).
Later on he started using more bb exercise in his training routine. I have no doubt that a prime Tyson would squat 405 for reps. Its not that heavy for a 220 athlete with thick legs.