Win Model 1200 question

I have a Winchester Model1200 stamped Modified. It had a dented barrel so I cut it down to 18 3/4". My question is, can I have a 'smith thread it to accept a screw in choke? I want to shoot #5-6 out of it for turkey hunting. What kind of pattern would I be looking at? Or would I be better off just buying a different shotgun? I really like the length just because it's more convenient to handle.