The hub was used from the 600EW to the 1938 Aero. The 350EW used a sheet metal hub, but around 1930 they lightweight models were using the same hub as the larger models. So quite a few models used that hub so it ought not be too hard to find some.
Your going to need brake drums and backing plates. Those did change over that time up to about 1932-33, then the design stabilized. After 1933 they would be cast iron drums rather than sheet steel, and the backing plates would have a slight overlapping water excluding lip, rather than being flush.
Big problem with the Douglas hubs is finding the obsolete taper roller bearings. There is a post you will find if you do a search about converting to a stronger axle and sealed ball bearings for these hubs.
-Doug