I have an Eastern Arms 101.7 5100. It's a 12 gauge sold through the Sears catalog in the mid-1930s. My gun and yours are indeed early Stevens 311's that were branded for sale through various department stores. The "case-hardening" was a chemical treatment that came off with powder solvent, so most of these guns don't have much, if any, color left.
Mine, like yours, shoots great. I've chopped the barrels to 18.5" and it makes a great coach gun for CAS. I'm quite sure it'll serve any purpose you desire in the field, though I have no idea about using it as a slug gun.
Here's a parts diagram, just in case you need it: http://www.e-gunparts.com/productschem. ... =089Zz5100
Good luck and enjoy your gun!