Welcome from Virginia! You seem to have a very nice piece. We will look forward to some pictures, but in the meantime you may be interested in the following info. Around here we use the Standard Catalog of Smith & Wesson as our "bible" so to speak on all things S&W. It is now on its 5th Edition and I looked up the Model 66 and found that it is probably one of the largest of the Model number revolvers that had "commemorative" issues for many, many, State Police, BATF, State Highway Patrols, County Sherrif Dept's, etc. In fact there are two pages of listings and the South Carolina Highway Patrol is one of them.
The current value is listed as $1000 for ANIB (As New In Box) meaning everything just as it was delivered and probably unfired. The problem is that there are so many commemoratives that it is a very specific collector that wants a South Carolina Highway Patrol gun to fill out his/her collection. This is the person you need to reach. Every day used Model 66-6 for example revolvers are bringing maybe $500 and even that is a hard sale. Mine was posted for sale for quite awhile before it sold, and mine had all the original box, documents, fired case.
Again, when you are able to post some pics that would help, but in the meantime just answer the following questions and the experts on this Forum will help you date it and maybe give a more accurate value estimate. We need to know the serial number, the barrel length (either 4" or 6"), the rear sight color (either stainless or black/blue), internal lock on left side of frame, wooden grips or rubber. All of these things help to correctly date your revolver. These guns were manufactured from 1970 to 2004, with the internal lock appearing after year 2000 approx. The internal lock is even less desirable than the earlier versions.
Edit to add info: I see where you did post that your uncle bought it in 1983 so for sure no internal lock, and it may have the longer barrel (6") and even wooden (Goncalo Alves wood) checkered Target style grips, making it more wanted than the internal lock versions later manufactured).