Here is some barrel evidence that suggests a 1949 d.o.m:
As far as I can tell, the "stepped" barrel is a 1950 development. Every 1949 that I can remember does not have the machined ring or step.
This if from yoopers site. Its a good side by side comparison photo. The "step" is hard to spot until you know where to look:
This is the barrel from the curious auction rifle:
Check your 1950, 45° gas port carbines. I checked mine, and it has the step.
The absence of the machined step on the auction carbine supports possible 1949 d.o.m. , imo.