daddeo,
On top of the transmission immediately behind the shift tower is a flat spot about 6 x 8 inches. On that space should be some cast in numbers with the foundry date code.
My '38 1-1/2 ton's have the following codes:
J 21 7 -> September 21, 1937
F 7 5 -> June 7, 1935 or 1945
The first number is from the truck with the original engine in it that doesn't appear to have ever been out of the truck.
In a recent publication from the National Corvette Restorers Society, there is an article about foundry marking on 'Vette intake manifolds. The tag used to make the date code indicates which SHIFT in foundry made the part by the shape of the screw heads holding the tag in place. Two flat heads -> 1st shift, 1 round head, 1 flat head -> 2nd shift and 2 round head for 3rd shift.
This was used at the Chevrolet Saginaw Foundry.
