I have some information regarding the serial #
51314xxxxx
The first digit tells the year (5)=45
The second and third identify the make and the series (13)=1/2 ton
The forth and fifth digits tells the body style
(14)=pick-up delivery
The balance of the serial # identifies the particular vehicle (xxxxx)
This information from a Canadian Chevrolet Maple Leaf Parts Catalogue series 11-18 1938-46