Bibb,
Welcome to the world of Parkers! The "G" under the watertable of the receiver just means it's a grade G as does the 2 above the serial number. I don't know why they double identified the grade that way.
You have a very valuable Parker if in good condition. We'd all like to see pictures of it. Take as many closeup in focus pictures of the watertable, receiver sides and bottom, the barrel flats, the stock, the muzzles, and the end of the rib where it terminates. Also if you would post the full serial number, we should be able to find it in the serialization book and tell you it's original configuration.
I don't know where Terrell Texas is in relation to where your at but Herschel Chaddick is a long time Parker collector and dealer.
http://www.chadicksltd.com/site/amshots.htm