Well M is the code for the 5th digit in the vin that signifies 440 for both Dart and 'cuda.
All 340, 383, 440 Darts are GTS cars. That's what makes the 440 'cuda much more special that a PLAIN old looking GTS Dart. No distinction rite off between a 340, 383, or 440 GTS until you get close enough to see the number in the hood inserts.
ALL '69 440 'cudas ARE 'cuda package, never made 440 Formula S Barracuda.