Hyper: Before I paint my bodies I set them on the car and mark where the posts are once I get the shell all squared up. If the body is already painted it's a lot tougher but you can use a bright light underneath the shell to kind of see the shadows from the posts (this way basically sucks IMO but if the body is painted, do what you have to do). Also, remember to make your holes before you peel off the overspray film or you'll lose the marks (done that once lol). If the holes are already screwed up, you can cover them with a sticker, fill the hole from the backside with shoe goo or something, and redrill your holes.

For me the absolute worst hole to cut is for my exhaust stinger but this is the drift thread so you probably don't have to worry about that. Hope this helps.