Ithaca M37 Vietnam Trench?

[K98kG43]

I picked this up a couple months back listed as a "WW2 Ithaca" but it's not. The serial number puts it right in the spot for the 1967 US Trench contract. It looks good parkerized with the dull stock and good looking stamps. Must of been a police gun at some point with the L.P.D. on the left side. It has the SP-30-06 marked bayonet mount that Rock Island Auction seems to think is right for Ithaca trenchs. My question is the Full Choke barrel. It has the divets for the heat shield screws and the front sight has a factory looking plug in it, but I've never seen a trench gun with a full choke. Anybody have any ideas?