I did a little further checking and found evidence that your gun may have been part of a recall. Serious injury resulting from the bolt hitting the shooters in the face was the basis of the recall.
I would urge you to check with a gunsmith who will be able to give you an estimate of it's worth and/or an opinion of it's danger.

http://www.google.com/search?hl=en&safe=off&q=583.19+j.+c.+higgi ns+20+gauge+recall+sears&start=0&sa=N