Your car is a 67 Dart GT convertible the and the core support and trunk lip decode like this:
7 is Dart
2 is Hamtramck
421 is the scheduled production date
03791 is the SO# that matches the fender tag lower right.
Any other questions? The 68 is the same except for the B is Hamtramck, 8 is 1968, and V is Valiant.