When you hear old timers talk about pitchers of today, they say they are lucky they never seen heat that "common" in the league. (they could also just be talking very modest)
And just look at their windups ... most of the funky windups could not incorporate that much velocity just for pure mechanics reasoning ... but it was more for deception of the release points.
But we will never know without a gun... all I know is the old videos I watched, the ball never popped like it does now. Or those small gloves they had, there would be many broken hands on the catchers.