The firewall stamping / stencil is the only guide for the older years for color or assembly plant. The VIN breakout is as mwarner shows.
I've discovered that a lot (but definitely not all) of the VIN numbers will have the assembly plant stamped at the end on the firewall tag. For instance, a lot of the Louisville trucks have LOU stamped after the VIN. In this case, the "CH" could very well mean the Chicago factory? That VIN number sequence is well within the 1950 range.