You got me a little there ;). A 68 or 69 Dart GTS 383 4 spd convertible in the right color combo would give a M-code a run for its money...actually I'm pretty sure a 383 4spd conv would sell for more.
But title and first sentence talks M-code.
Not why a /6 belvedere with an added Hemi should sell for the same price as a number matching original. Nor about the rebody debate.