If the stock is gloss walnut it is not an Express, or the stock has been changed. All Express guns have a matte finish on the metal and either a plastic stock or cheap hardwood stock with reverse stamped checkering. I did see a handful of 870 Express guns sold at K-Mart years ago with real walnut, but they still had dull finishes and reverse stamped checkering.
A Wingmaster will have walnut stocks. Guns made within the last 20 years or so have real checkering, older guns used the reverse stamp. All Wingmasters will have polished blue metal.
If the barrel is from the factory there is a date stamp on the barrel that can be looked up here for date of manufacture. If the barrel is not original you'll need to contact Remington with the SN for an accurate date.
Regardless, if it is in good shape it is easliy worth $250