So, there seems to e two possible answers here.

1. Chrysler changed the type of light at some point during the model year, so the hard tops COULD have either style. ALL of the five HT's I've owned had the one piece non-screw style cover. Two of those were bought in the 60's so I know they weren't changed and the other three still had the original headliner and no indication that the light assemblies would have been changed (screw hole for screw in style cover).
2. The other possibility is that the 64 HTs with the later style cover had had there's changed at some point in the past since the replacements for the one piece style are not available.

I'm going to guess option 1, since a late year change in parts is know to have happened in other cases. I'll have to look at my parts book to see if two different part numbers are listed for the two door hard top models.