OK, The oval hole in the firewall is fixed position. Where the motors shaft is positioned in that hole does change with mfgr and type. Mismatched linkage parts would try to pull apart or jamb the linkage.
They didn't or couldn't dictate that all power steering pump mfgrs make those all the same either. Cost? Patents? Who knows? They simply produced brackets, pulleys, etc.., for each pump mfgr/type.
