1970 Dart Swinger 340 4-Speed FC7 Plum Crazy!! YUMMY!!!

Fender tag says D13 for the trans. Wouldn't that be a 3 speed and not a 4? (here I go asking A body questions again) For B and E body cars a 4 speed is a D21 code

Correct, same for A's
D21 = 4 speed
D13 = 3 speed on floor