Cut it down? you mean the barrel; it's 20 inch. all of the internal action parts minus springs/levers/firing pin... are "chrome/nickel" finished; even the trigger assembly matches the outer finish looks to me like factory. I also only paid about $270 for the gun from a store. if someone paid to finish the gun like this it would cost more than its worth.
Winchester 1300 Marine. I recall a Marine model but don't remember it having wood stocks. It was bright nickel like yours though. It's definitely a Model 1300, in whatever incarnation. The shorter models like this were Winchester's offering to L/E to compete with the Remington 870 and Mossberg 500.