Andy, I believe you are correct about the 390 "Sporting" model being a clays version. It has the wide rib and a magazine cut-off, matte black barrel and walnut stock.
I got it at a hardware store/sporting goods store (I avoid those wal-martians whenever possible) $525 cause it was the last one they had and the 391s were in, and because I've done business with the mom-and-pop outfit whenever I could.
Side note: at this store, I once walked in and bought hardware for my antique 1927 model T Ford touring car's top. I walked in and said "I know you don't have... but I'm looking for.... and they did. Made me a loyal customer and an anti-Wal-martian.