Welcome Tom. I also have two that are 50 years apart, a 1953 panel and a 2003 GMC van. They are painted exactly the same colour and are sometimes together at the jobsite. Why don't you take the colour code from the newer truck and paint the '57 that colour when its ready to paint?

http://s365.photobucket.com/user/1953panel/media/DSC01845.jpg.html?sort=3&o=15

Leo