I think you got a nice shotgun there. It even still has some of the red paint on the safety button.

620 trench guns are not all that common compared to the other models, except for the WW2 Ithaca trench guns.

One question: In one of your photos, the two spot welds that attach the heat shield to the bayonet adaptor look a bit strange. It may just be the photo. But they should be fairly smooth.