Old 20 gauge/new barrel

[B-47]

I have an old 20 gauge Wingmaster I bought in the early 1980's and I want to configure it for home defense with a shorter barrel. This is from back in the day when the 20 gauges were built on a 12 gauge frame. The way I figured this out is because a new 12 gauge fore-end fits on it perfectly (the good news). Does this mean that a new 20-gauge barrel WON'T fit it (the bad news)? If so, any ideas as to how I can set it up with an 18-20 inch barrel?

-B

[Synchronizor]

What letter does the gun's serial number end in? I believe the large-frame 20ga 870s had serial numbers that ended in "X" or "N".

As far as I know, you will need a large-frame 20ga barrel for a large-frame gun. Auction sites like Gunbroker and Ebay may have used ones for sale; and if you're having trouble finding an 18-20" one, you can always cut a longer barrel down to the length you want.