I came across a barrel and forearm assembly for a Winchester Model 12 16 gauge. I thought it would be nice to have an extra barrel for my Model 12 so i am thinking about buying it. What work is required to get this assembly to fit my shotgun. My gun is a proof steel gun from the late 30's while this barrel I found is an older nickel steel assembly from the mid 20's. Tell me what i would have to do to get it to work on my gun and how much it might cost. Thanks!