Over on the AD truck side we depend on the assembly manuals to figure out where the spot welds are quite a bit and the manuals usually have the exact measurements you need when you are working on the body or chassis. Worth the 30 something bucks if you are going to do much panel removal/replacement.
This is just for example
http://www.ebay.com/itm/1967-1972-CH...8e419c&vxp=mtr
There are a lot of them for sale by different vendors on Ebay and they can be bought through Amazon.
There it might make more sense now.