shaner,
Serial number puts it as first year that C prefix was used or 1948.
Looking over your post you never mentioned caliber...is this a 38 special, a 38 S&W or a 22lr?
Is this a steel frame or aluminum?
The C prefix serial number was used on the following:
Pre model 10, in 38 special. (most likely, "old M&P" as you suggested).
Pre model 11, in 38 S&W.
Pre model 12, in 38 special with airwieght alum frame.
Pre model 45, in 22 lr.
Let me know which you have and I may have more info on your gun.
HTH
Fred