Mike D, As I try to mesh your input (great reference!) with the input from Cosine26, I arrive at the following conclusion: The NM configuration 1903 that I have was possibly drilled for a receiver sight by some organization (unknown or Springfield Armory) who did this for the DCM or it could have been what you refer to as "kinda bubba'd" by a previous owner. Since my gun has the drawing numbers on the butt stock (C-style) and the hand guard as well as a star gauged barrel, I am assuming my gun came from the DCM, but I understand that it could also have been a gun that someone put together from parts and even drilled the receiver for a sight. If the latter happened, I find it strange that the person would have 'settled for' a Redfield sight instead of a Lyman, but I guess that is also a possibility.
Thanks for the great information. It has been very enlightening.