I'm going to just guess on this, but, the value of this particular Parker isn't going to be decided by it's grade, condition, or originality.
It was Burt Spillar's gun. William Tapply owned it most of his life. The gun has a history of use by one of, if not "The" high priests of ruffed grouse hunting, during the golden era of ruffed grouse shooting, in the Mecca of ruffed grouse hunting.
I'm going to guess that we will be stunned by what the gun sells for. I'd guess in the middle of five figures.
Best,
Ted