You will find varying input on this but for the sake of looking as close to factory the splatter paint was sprayed on heavy and usually over Floor pan, Wheel Tubs, Quarters and even as far in as to get on the lower portion of the shelf braces. You will also find some original cars with light over-spray on the light-houses. This like ANY process was not exact on each and every car and/or assembly plant. It was a quick get it done process on a "keep it moving" assembly line so you really can't be too wrong with application.
If you don't have access to spray, the EASTWOODs spray boom trunk paint is excellent! I just re-did the trunk of a '67 and it came out great.
GTO Jr. - A.K.A. SPRINT 6