Cool. I've thought about doing something similar myself, but the right gun never turned up. It's probably way too pricey for a 'just for fun' project, but this site has the original Win97 heatshield and bayo lug for sale. It could probably be fitted with a little work. Winchester 97 Trench Gun Bayonet lug & Heat Shield w/ Screws
Actually, I just so happen to have one of those which is an Ordnance-marked trench gun. The action was locked up when I got it, and after I took it apart I figured out why: someone had been tampering with the internals, grinding some surfaces down. It's just been sitting since I can't find parts for it, though. Stock was replaced with what may be a Winchester stock, too. It needs some TLC as well, but would make a genuine finished product. So if you have some spare parts, I may be interested, if you want a genuine 620 trench gun, though, this one might work better for you than for me.
Whats the Ordnance - mark? I think I may have a trench Winc M-97. I think it had a heatshield like the one posted above with link. Because where it is connected just above the pump there is blueing missing on both sides where it clamps on above pump.
Just found it, Has the U.S on the side of receiver and the flaming bomb. Mine does not
I'm going to dura coat it, too pitted in spots to blue it, plus the tactical black will look cool. Bayonet lug/heat shield is going to be a while, too much other stuff I want to get beofore dropping $125 on somthing that won't get used much.