Keep in mind unless you plan on keeping this gun for personal use, restoration may take away value from your shotgun. Especially a Parker or Fox. I have a Fox that could use some work but I chose not to in fear of losing value.
JRD correctly stated that restoration "may" decrease the value of a gun. I agree. Most gun shops would consider restoration as synonymous with stock refinishing, recut the checkering and rebluing. This is absolutely incorrect.
Proper restoration should be limited to any required mechanical repairs, restoration of the checkering to match the existing worn checkering, repair of worn bluing with a few light coats of a slow rust process and restoration of the stock color without stripping the existing worn finish.
Any antique that does nor retain the patina accumulated over many years is suspect and typically does command a lower value.