ignoring, for a moment that it would have been far more intelligent to post this in the STEVENS forum, since I saw it only by happenstance...
The 311 was made for a lot of years, and your description is not sufficiently detailed to let us date the gun.
And, your definition of "great" might be different than a collectors.
That said, 311's tend to sell in the range of $200 to $500 depending on the fussy details of condition, age and gauge.
Your 12 guage is the least desirable because it is the most common.
See http://www.gunvaluesboard.com/firearms-reference-file- stevens-323.html
for details of dating the gun.