[jonzcustomshop]

The next group of numbers is the Serial number or unit built number, all series at all plants
started with Serial number 1001. For the 1966 year run, GMC started most series with Serial
number 10,001, but some series not used in 1965 started with 1001. I have found that GMC had
a lot of left over trucks from 1965 & they sold them NEW in 1966 as 1966 Models, this was
done to rid the dealers of any older trucks still on the lot to make way for the NEW body
Style coming in 1967. If you have a GMC "PF" or "ZF" series truck titled as a 1966, but the
Serial number is lower then 10,000, it mite really be a 1965 model year truck. One way to
tell is to check the engine for a spin-on oil filter, no spin-on filter, then it's a 1965.
GMC swithed to the spin-on oil filter for the 1966 model year on V6 powered trucks.

with that in mind...yours should be the 1171st built that year.