-64 A body manual steering box

Hi. What is the difference between -66 onward manual steering box and pre -66 one? In this case -64 one. I would like to renew my -64 Dart steering box but only -66 onward boxes for sale on Ebay. Or can the box be fixed to get rid of the loose feeling and steering wheel free play. I am in Europe so no US shops available. And this should be done at reasonable price.