Changing the rear quarters on my Dart conv. from a 69 to a 70

If I recall correctly, my 70 340 Dart Swinger had the same head rest as the 69' GTS, not the 69' Swinger ones, that are more squared off. If your finish project is to be a 340 convertible, then I would say it would be called a GTS, which also was not a 70' option.
Going to put 70 style bucket seats in it possibly with a 4 speed.