The vice was a vintage machinist vice with a 4" width and the casting that broke was a 1/4" thick 2" x 4" C-channel of cast iron. I will still say it was the wrong tool for the job but it is the only vice have (had). You can place an incredible amount of force with a 24" vintage Rigid pipe wrench. I have crushed 4" cast iron heating pipe with it without it breaking loose.

Out of curiosity, is Pitman arm and accurate name when referring to rack and pinion steering and single control arm.

Edit: Just to be clear, I successfully removed everything from the car, I just needed to remove the outer ends to fit the core back in the box without issue. They cannot be separated without heat and a bigger vice.