Using a three foot bar, and applying 58lbs in weight on the end, would result in applying 174ftlbs to the nut.
For 400ftlbs, applying 100lbs to a 4' bar would equate to 400ftlbs. As I weigh 210lbs (15stone), if I stood on a set of scales whilst leaning on said bar (it would need to be in a horizontal position) I would need to see 110lbs reading on the scales to know I was applying 100lbs at four feet from the nut = 400ftlbs.
In all instances the applied weight needs to be made when the bar is horizontal to the ground. Any deviation from horizontal will reduce the effort as applied (presuming the scales were in use).
It's all just mathematics.