The std Dart with 340 thermal 2707 has an overall length of 3.60 inches from water pump flange to end of thermal clutch, and a length of 2.03 inches from water pump flange to fan mount surface.
The Dart with 340 heavy duty thermal 2747 has an overall length of 3.34 inches from water pump flange to end of thermal clutch, and a length of 1.62 inches from water pump flange to fan mount surface.
The heavy duty 2731 "Cadillac application" has an overall length of 3.97 inches from water pump flange to end of thermal clutch, and a length of 2.25 inches from water pump flange to fan mount surface.
The 2731 placed the fan mid span on the blades in my reproduction shroud where is should be.