Well, make sure it is chambered for 3", because a lot of early Wingmasters were not. It will be lighter in the same length, and the top of the rib - if it is ribbed - will have anti glare finish as opposed to the same finish as the rest of the Express. And several million of them were made before RemChokes came on the scene.
You can shoot slugs thru any Rem barrel(slug barrel or not). Most would certainly shoot better using a slug barrel. Virginian is correct about some of the early 870 barrels being 2-3/4" only. Rumor has it that at some point Remington changed to chambering all 870 barrels to 3" but marked some 2-3/4" when sold with a non-magnum gun. I never bothered to verify this rumor.
Also Rem did make the Special Field in 12 gauge which took a special barrel.