Here is the link where I found the info
http://service.gm.com/dealerworld/vi.../vincard79.pdf
C = Chevy
1 = 4x2
6 = 16,000 - 25,000 GVW range (C-60 series)
D = 97.5 BBC Conventional Cab
A = 350 engine
9 = Model Year
V = Assembly Plant (I think GM Truck Pontiac)