What is "improved" strut rod bushing?

Parts man said he would order both sets and let me pick out which one I wanted. Does anyone know the difference (other than the price!)? This is on a 65 New Yorker. Thanks-Pat

Might be one rubber and one poly/plastic of some sort???

The improved strut rod bushing is 2 pucks that sandwich the K-frame. It comes with new washers/plates that are installed in the opposite direction to the original ones (ie cup out). I guess it allows for more strut bar movement with less rubber deflection.