If its in as good a condition as you indicated grab it.
Even at $400 its a good price.
Barrel does not have a serial number, you check the mfg barrel date and then see what date the serial number is for produciton (that will come up with a month and year)
OEM barrel will be within a month or two of the receiver date.
Other item to check is what stock it has. On the for-end there will be an E, R or W (possibly nothing, there seems to have been original stocks made that did not get a mfg stamp, in my limited looking I have seen two of them now and they were old and matched the gun).
If you buy it PM me and I will send you links on sights that can get you parts, how to dissemble the gun and the bolt and ID of various parts and where the markings should be on them.
Best match collector wise if the barrel and receiver are same mfg.
WWII barrel least desirable, you do find a lot that have good barrels and receivers that do not match up mfg. They were redone so much in various calibers that spare barrels were around and someone would convert them back.