Nick - many thanks, you're not poaching at all. I intended it as a general question, with just a tug of the forelock to the venerable Les who is like one of the Gods on Olympus with respect to these things.
The adapter ring was a Heavystar item on the Bay and I ordered it with the vented hood. Just checked - here is the link - http://www.ebay.com/itm/New-Metal-Hood-for-Leica-Summitar-50mm-f-2-0-/360470341358?pt=LH_DefaultDomain_0&hash=item53edb4e6ee#ht_500wt_1367
If that link is broken just search on "New Metal Hood for Leica Summitar 50mm f/2.0" the package I ordered is now listed at $US27.95 and includes:
This auction includes:
One (1) adapter ring Leica E39 Filter to Leica Summitar 50mm f/2.0 lens mounting
One (1) 39mm screw in metal vented and tilted hood.
One (1) lens cap on the front hood.
I like the lens cap on the hood - works well. The hood looks much like the regular one for the Summicron 50 but is more secure for being screwed in - nad the E39 filter adapter ring is useful for other things - not the same quality as Leica adapter rings & filters but ok for the price - seems like light aluminium