Chevrolet Models made from 1942 through 1945 all had the same engine and rear axle prefix codes.
Based on the info provided it would seem like your truck is a 1945 model.
Your engine is BD747xxx making it the 746xxxth engine made out of the Flint Engine Plant (starting at 1001). This would probably put your engine into 1945 when it was assembled. Look for a cast date code on the passenger side of the engine block.
The Rear Axle is coded by 'calendar days', so 1690 would put in into mid May 1945 assuming the 1942 model started October of 1941.
The transmission will also be stamped, but it will be on top by the edge of the cover (hard to see with it in the truck.
Mike B
