Frank, I'm going to say no in answer to your question. In looking through various Chevy parts books, here is what I found for the Conventional Cab Assembly (CCab) for the years 1939-46.
1939-40 is listed in the 1929-41 Chevy Master Parts Price List as part# 604477 (see 1st pic below). Appears the same cab used with different instrument panels depending on the year as mentioned in NOTE III (see 2nd pic).
In the same resource book, the 1941 CCab part number is listed as 605237. The book shows no relation between the 1939-40 CCab's and the 1941 CCab.
The part number for the 1941-46 CCab's would change in the 1929-46 Chevrolet Master Parts Price List to 607029. It then again changed in the 1929-48 Chevrolet Master Parts Catalog to 3847013 for 1941-46 CCab's and remained with that part number through the 1929-54 Chevrolet Master Parts and Accessories Catalog. The listing for the 1941-46 CCab parts disappeared from the 1929-57 Chevrolet Master Parts and Accessories Catalog.
Just my $.02 worth, but if you want to pursue the cab with seller, get them to provide many more pics to helped figure out exactly what it is. If still present, there should be a data plate on the cab which would help define what it is. Good luck.
