bucket seats with headrests are probably your safest option. I would also recommend upgrading the seat belts with a later model version with shoulder straps. 65'
(On the '67 and early 2 door cars , the seatbacks fold forward and have no latch)
Headrest is definately a good safety feature. You can't go wrong there.
Hilderbrand1983 has brought up a good point about the safety aspects of headrests versus no headrests as has Plym65 concerning shoulder belts and Mattax about latches on 67-earlier buckets. Bringing up these concerns has got he thinking about my own 65 Dart 2 door sedan delivery project. I will bring up these points and possible solutions applicable to my project on my resto thread. Thanks to all for bringing these points up.