1973 360

Found a weight for a 1970 Swinger 340 - 3170#.

https://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1970/70_Dart0028.jpg

105# lighter than a 1970 Duster 340 or 225# lighter than a 1974 Duster 360 and 240# lighter than a 1974 Dart Sport 360.