It depends somewhat on how accurate you want your replica. If you want it exact, then you'll almost need to have an original at your side the entire time you are fabricating panels. If you want to get "close" but are not a stickler for exact detail, what I do is us a plastic model (like Revell etc) and then scale up each measurement by the scale indicated on the box (most are 24:1 I think). That's basically what I did to create this '31 roadster. There are some places around the internet where basic body and frame measurements are shown. Perhaps another of our members has a link or two they can provide.