I am looking at buying a Stevens 520-30 Trench Gun that is missing its handguard/bayo lug. I found a very good deal on an original guard, so I am set there. What strikes me is the receiver has either a very light parkerized finish or maybe Military Finish and the barrel and slide have a heavier parkerized finish. Dealer refers to the barrel as "reparkerized," but he does not know when. No way to tell if parts match. The dealer has pics on his website, but he is traveling out of country now. SN is in the 69000 range (late WW II?). Could just the barrel assembly been parkerized for Korea or Vietnam? I have read that the late war aerial gunnery practice Stevens wee parkerized. Any thoughts?