FWIW, I have an older 870 Remington Wingmaster made up into a very nice trap gun that sports among other custom work a Winchester type doughnut w/post rib. The treatment [rib's top finish & the receiver milling] appears identical to that shown on your 42. The rib is clearly marked "Simmons Gun Specialties .... Kansas" on it's left side.

Last edited by tw; 10/11/13 08:14 PM. Reason: Spelling, but also to say that your 42 is indeed a VERY nice up-graded gun!