Comparison with OPs REG 4923 with REG 1530 (a 6"er in my collection)
... and for reference, this is the side profile of a King Reflector Ramp (from another RM):
Nframe29:
First of all - CONGRATS!!! What a fun gun and for the money, it would be in my safe if I had come across it.
Consistent with comments above, my observations after looking at 100's and perhaps more than 1000 pre-war magnums:
1. Post war parts for sure include the rear sight, grips, and extractor rod.
2. The barrel appears to be a post war barrel as well- no large knob cut out (that I can see from the photo), post war large front ramp, and no rebated front sight (that I can see from the photo) i.e. the front of the sight base looks to be flush with the crown of the barrel (not rebated 1/16" - 1/8" like the pre-war front sight bases).
3. Well-used and a super fun shooter!!!
I LOVE THESE KINDS OF GUNS - lots of fun anomalies to investigate and sleuth out.

You have some of the best resources available weighing in on your gun:
Mike (first-model) is a trained historian with a passion for all things S&W, and as a leader in the S&W Historical Foundation, he has access to all of the scanned S&W document archives. He is a great resource to all of us collectors.
Terry (lester357) is the keeper of the SWCA pre-war Magnum and Transitional Magnum databases. He is passionate about collecting and cataloging the current condition of as many of these great guns as possible and he too is a great resource to us collectors.
That both of them have weighed in on this gun, would indicate that your RM (although not a pure specimen) is AN INTERESTING GUN!
Although not in the same league as Mike and Terry, I have a passion for the pre-war and early post war 357 Magnums and have a collection of quite a few of them. In addition, I have collected many photos of these guns over the years and refer to that photo database regularly. Here are some of my observations to Mike and Terry's dialogue above:
Mike:
From the one photo that I see, that barrel does NOT have the cut out for the pre-war large knob. And the front sight ramp base is consistent with a Post War barrel (longer base) and most pre-war ramp bases were King bases. The pre-war Patridge sighted barrels typically had the square base, rather than a ramped base (unless it was a King ramped base). I see this as an early post war replacement barrel (some of which still have the Large knob cut out in the shroud). I would love to see photos of the shroud, and the frame with the grips off.
Terry:
The roll marks on that barrel are more consistent with pre-war roll marks, but not unknown on post war barrels (as noted by some of the ones that we have recently discussed). Roll marks are not even 100% consistent with the magnums of the same era, with slight variances front or back observed regularly.
Lots of rambling from me, that I'll probably edit when I have time to read it again.
Once again - FUN GUN! And Thanks to all for Sharing,