95% original condition 42 solid rib skeet ought to bring between $3.5k and $5.5k in today's market. Lot higher couple years ago. Saw a postwar bring $8k awhile back. Anyway, should have "skeet" choke. A 2.5" chamber increases value, as does prewar. A vent rib gun, if original, would bring more. Most VRs on market are not original, tho.
95% original condition 42 solid rib field ought to bring between $2.5k and $3.5k, today's market. Prewars bring a bit more. IC least common. Cyl pretty uncommon. Mod slight premium. Full most common.
Poulinantiques.com has a searchable auction history. Give you some idea.