The square instruments indicate late 40's, is the hood the steep V shape or flatter V? the hood was changed after 48. The rear window size went from small to full width in 53. The tailgate had the WO stamp until 53 when Kaiser bought out Willys-overland. Not sure on the ashtray though. Maybe with some of the visual cues it will help date your truck, but remember that the year of manufacture and the year of title are not always the same, many were titled in whatever year they were sold.
So if yours is original 49 it should have the steep V grill, the small rear window, and if you got lucky the WO tailgate.