35truck, I did a little research through my resource documents. The casting# 838533 is indeed a 1 year only 1937 Truck only (Commercial and Utility) bell housing (see 1st pic below from 1929-54 Chevy Master Parts Book). The one in the eBay ad is the same casting number, but they have misidentified it with the 1940-49 application years. Not unusual for that to happen.
On the starter, according to a 1929-48 Delco Remy Catalog (see 2nd pic), the one year only 1937 starter is correctly ID'd as a 739-A. But the picture in the catalog shows it with a small starter drive gear. The catalog breaks down the individual part numbers of the starter components, but unfortunately doesn't give dimensions (see pic 3). The 4th picture just provides part number confirmation between the Delco Remy catalog and the Chevy Parts Book for the end frame housing and starter drive.
A quick web search for 739-A found one rebuilder offering a
https://www.ebay.com/itm/266626030194. The asking price is up there, but considering it is a one year only, not hard to see how it got there. Hope this info may provide some help with your question.
