Looks just like a Win63!
My great uncle had a 63 that I learned to shoot with. Been looking for a nice example for years, but man, are they expensive! When Taurus started making a 63 clone, I had to pick one up. It's a decent shooter, and a pretty true replica, but it's sure not a Winchester!
Did Winchester ever make an auto-loader carbine of a similar design in a currently popular center-fire caliber? Something just like that in .38spl would be just the ticket.
Nice find!