1970 Dart Swinger options question

[Al Bundy]

hi,I am looking at a very clean 1970 swinger with air conditioning and noticed it has the plastic style ac vents. My old 70 has the earlier chrome style. The car is a one owner original,did they switch to the plastic vents mid year? It has the five button ac control panel,so it's not aftermarket. Also did all swingers come with headrests or were they optional?

 

[Al Bundy]

Nobody here knows anything about when the changeover occurred from the chrome ac vents to the plastic?
I ask because I have seen both types in 1970 swingers leading me to think they may have switched mid year?
Anyone here know for sure?