here's what I deciphered from
www.6066gmc.org/ :
10=1/2 ton
02=127" wheelbase
P= pontiac michigan assembly plant
F= 64-66 model year* see the pharagraph below for more on the F code.
6261= sequential production #
A=6000 pounds or less GVW
*The series letter for 1964 to 1966 is "F". There was not any
more major changes for this body style. But there was a series letter "E" used on some
1965 trucks (have not seen any yet) & "D" used on all inline engined 1966 trucks. More
info has been found for "F" Series Trucks, GMC built truck in two plants from 1964 to
1966, the Pontiac Michigan plant & one of two plants in California, Oakland or Fremont.
If your trucks vin shows "HF" it was built in the Oakland California plant which GMC shut
down after the 1964 Model year, so all "HF" trucks are 1964. Production was moved to an
ALL NEW plant built in Fremont California for 1965, so "ZF" trucks are 1965 or 1966.
So here is a brake down of the series letters;
N = 1960-1961, J = 1962, G = 1963, F =1964-1966, E = 1965, D = 1966