Kev,
If by flared end you mean at the gland nuts, I do not think they rolled the edge of the tube from the factory. Or if they did, the design was superseded on later EWs. See this post:
https://www.douglasmotorcycles.net/index.php?topic=1786.msg6419#msg6419The Flanged Collars (#1008-1) slip on, and make plating the gland nuts and manifold a little simpler. You still have the ally muff that the plater has to mask-off. There are still enough EW inlet manifold about that I do not think anyone has gone to great extents to salvage one that is really rusted.
The hub in the eBay listing is a for the detachable brake drum models. They came along a little later, first on the rear and then both ends. It is a similar hub to that used on the CW, but there the conical spline was narrower and just used for mounting the sprocket.
The EW spares list shows a common part number for the front and rear brake backing plate.
-Doug