the numbers only relate to whatever the GM office team was smokin that day
the "x000" designations were earlier years, as Fumblin lists - the C, K, etc numbering started in the 60's and the 10's were 1/2T, 20's = 3/4T, 30's = 1T - the C=conventional 2wheel drive, K=4x4, P=panel or walkin deliv
C/K10 would be the short 1/2T series, C/K15 = long 1/2T and that numbering gets pretty complex adding all the variations of weight, length, 4x4, etc, complicated by the fact that the "C10" is the series, but followed by 2 more numbers indicating the exact model, so a C1434 is a conventional 2WD short 1/2T pickup
GMC used entirely different numbering
Bill
