Thank you for the question Chuck.
Yard trees, regardless of species, are a mixed bag for most timber buyers. Root damage, defects to the bole, and potential metal in the tree often deter most interested buyers from coming out and looking at most yard trees. Occasionally, some homeowners receive a great price for a yard tree.
My recommendation is to contact the Pennsylvania Department of Conservation and Natural Resources, Bureau of Forestry service forester who covers the county in SE Pennsylvania where your father lives http://www.dcnr.state.pa.us/forestry/serviceforesters_select.aspx Simply ask the service forester to provide you with a list of professional consulting foresters or local timber buyers who work in the general area where you father lives.
Sorry Chuck, but this is all the help I can provide regarding technical assistance in Pennsylvania.
Regards, Jay