That's what I was assuming too,but am not sure. I was thinking Chrysler,knowing the belts would be mandatory mid year would have had the mounting areas installed on all the cars in anticipation of it.
My buddy has a 68 also and he put a new headliner in and noticed the bolt holes welded in place and came over to look at mine he now has them in his car he had to buy new clips for the sun visor as they didn’t have the seat belt clips