You DO NOT need to buy any AutoCad program.....there is NO WAY that you can model an existing truck well enough for the program to have ANY usefulness during a build. IF you had a contact at GM, you could get the CAD models and use that but the body is not modeled in a format that is AutoCad compatible......forget the computer, just use a pencil and paper and write down every part and every operation. When you add estimated costs to your document you will have a $$ figure to shoot for as a budget. To be honest, for that truck in that condition, I would budget $45,000 as a minimum. Next, go see what you can buy a cherry truck of similar vintage for.....probably $10,000. I would suggest starting with a cherry body.....cheaper in the long run.