Yea.. the 'series' numbers that I mentioned above started in 1947 and were used up until at least 1959, when they were replaced with the 10 20 30 series numbers that started with a C or K to specify 2wd or 4wd.
Not sure when they started it, but I had a '67 'C10'.. so it had to have been between 1960 and 1967 they started that.
Then at some point.. in the late 80's (maybe 1988?) they appear to have dropped the 10 20 30 and went with 1500 for 1/2 ton, 2500 for 3/4 ton using C or K to indicate 2wd or 4wd.. at least for the 'full size' trucks.
