Just some anecdotal evidence from years of looking at these trucks, I would say that 1960 is indeed a more rare year for the 60-66 series. There seem to be many more 1961's that survived than the '60 models. 63-66 seem to be pretty heavily represented. But 1962's seem to be under-represented as well.
To me the really rare ones are the 60 and 61 GMC's and even more rare are those early GMC's with lots of side trim and chrome window surrounds, SWB's with big back windows. I'm talking strictly pickups here. I suppose a SWB 1/2 ton 4x4 GMC trimmed out and with a big back window and a Hydromatic would about as rare as you could get. Especially considering that that combination may not have even been available!:)
