The barrel and receiver have matching serials 84320V, it's also marked full, has R.E.P circled, and a weird little marking that just looks kinda like a leaf.
Oops sorry I was mis-reading your code as AAX rather than the AXX you wrote. That *would* be March of 1951, which would really make it the first production run of the then-new Model 870 Wingmaster shotgun!
Wingmasters are great shotguns, but extremely common. Most old hunting 870s are not worth any premium due to their antiquity, but this one has potential, or is at least interesting and appealing. Condition and original parts will dictate if it has any real increase in value.
Has the gun been used a lot? Is the finish worn completely off (or maybe it has been re-blued somewhere along the line). What about the condition of the wood? If it was hunted, you'll probably find ancient mud under the fore-end on dis-assembly.
Too bad it has been personalized. It was probably grandpa's gun, and engraved when it was passed down. The trigger group can easily be switched, but it won't be original.
The barrel is a Full choke that is not very desireable now, what is it, 28" long? At least it's the original barrel, matching the early receiver. No raised rib, probably just a lined rib along the top to cut glare? Is there a Poly-Choke installed (that would have been a common modification)?
I have a similar 870 from '51 with a slightly lower number than yours. (Doubtful that the numbering started at #1 — more likely 10001 or like that — so your gun isn't necessarily the 84 thousandth gun produced, but somewhere below that.) That gun is the grand-pappy of some 13 million or so other 870s!
Originally your gun would use a short ejector, which won't work with 3" shells even if you put on a barrel with the 76mm chamber. Many such guns that have visited a smith in their lives have had the later ejector installed as routine maintenance. (3,5" will never work in it.) There are other small differences that will also identify it as an older version.
Other things on the barrel are proving marks, meaning that it's been inspected and tested [more than] safe to fire.