Question about 1968 Dart shoulder belts

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
Cool. So it would appear I could add shoulder belts to mine then sometime in the future. I figured Chrysler would have just had the mounting holes on all the roofs in case someone ordered them and for when the mandate took effecf.