steering box problem ???

have a 72 340 demon. when driving down road, continuallyhave to correct strg. right to left when on center.took it in for a alighnment and the mechanic
said someone had messed with the takeup adj.,so i need a new pwr. steering
box. what kind of an adj.,if any,can i make.or should i look for something else.
front end has been rebuilt. do i really need a new box? oh ,yes. just bought car a few months ago.
thanks.