I just bought a Trooper MKIII and I am looking for some factory walnut target grips. There seems to be a couple of different versions. One has the checkering all the way to the bottom, the others have a distinct panel that does not go to the bottom. I have not been able to find my revolver in the serial numbers bases online as well. 760**L I am guessing '79 or '80. What style grips would be correct for the year?