That "inset" part of the box is interesting, never saw one like that. Does it look like it was "customized" by Joe Xacto?
There must have been a decent run of 6" barrels in that range, mine are on both sides of that one at 150-48881 and 150-53048 with no other guns between those #'s.
The 48881 is the first .357 I ever shot, my dad bought it new in the early 70's. He kept his boxes and the box is in better shape than the gun which has been fire a whole bunch and has pretty thin blue at this point.
53048 is this one with the funky cherry cylinder: