That is not the original box for that gun. I have never seen a factory label that was done in red ink. A gun with target stocks would not fit in a standard box as you have noted. Typically target stocked guns were in display cases in a sleeve. There were no over-sized boxes for target stocked guns that I have ever seen.
A 6 1/2" barrel is not "unusual, it was one of the standard lengths at the time, 3 1/2", 4", 5", 6", 6 1/2" and 8 3/8". I have owned several S&Ws with 6 1/2" barrels of several models. It was not until later that the 6'' was standardized and the 6 1/2" and 5" barrel lengths deleted.