model type info.

How do you go about to find out the exact model type your truck is. I have a 72' GMC, that I just got. I know its the basic 1/2 ton, blah, blah, but like I have saddle tanks plus the main. The emblems on the front fenders are there but missing the "1500 v-eight,1500 custom, 1500 super custom, 1500 sierra, 1500 sierra grande. Is there such a thing to tell you everything that was ordered on a particular truck by the trucks Vin #? Anything would help, Thanks