heres ones i got 1963 c10 fender emblem and not sure on the years of the gmc but its the v6 hood emblem:
heres some measurements
1963 c10 has two mounting screws with a measurement of 2 3/8
gmc v6 hood emblem has a guide pin and one mounting screw measures 1 5/8 and a part number 2419879 stamped on it
then I also have a cowl extension from a 1962 c10 with measurements for the holes hooking the straight hood side to the holes is 2 7/16 and then 7 11/16
then for the first hole measuring up from the crown for the first hole closest to the hood is 1"
then the second hole closest to the door is 1 7/8