Think the model number should be on the barrel at the breech. You could contact Winchester/ Browning and give them the serial and they should be able to tell you all about your gun
Got to be careful when buying these days, I bought an AYA side by side a few years ago and was told it was the No3, well when I emailed the manufacturer so I could find out when it was built they told me it was the yeoman and not the No3, main difference being the raised rib, didn't **** me off too much as it's a bloody good gun regardless. Find the main Winchester dealer or even the main company themselves and just ask. I even emailed Baikal about an old o/u I had (my first gun) and even they got back to me. Albeit in slightly poor English but they made the effort!