In searching for a suitable plug for my R69S with R69 pistons, here is what I learned from NGK:
1. B9HS-10 (3626), my first choice, has been superseded to a resistor plug, BR9HS-10 (4551). The non-resistor 3626 is still around but not easy to find. I ordered a set from Harvard Marine through Amazon, but they never arrived and the seller never responded, so I canceled the order and am waiting for a refund.
Footnote: The Harvard Marine shipment finally arrived and it contained the 4551 resistor plugs, not the 3626 B9HS version. When I told the company's customer rep that I had received the wrong plugs, he basically told me to f---off, but I did get a refund and was told to keep the incorrect plugs.
2. NGK B8HS (5510), which would have been my second choice, has been superseded to resistor version B
R8HS (4322). The 5510 non-resistor version is still around but it is not easily available.
3. NGK B8HS-10 (5126) comes out of the box gapped at .040. To my surprise, NGK tech support advises that "the maximum you can move the ground electrode is .012 +/-. anything beyond that can compromise the weld and can cause the ground to break off." I need a gap of .024, achieving which would exceed that maximum tweak. It would probably be OK, but I would not like to be a test case.
As suggested here in this discussion, I also considered the Champion L77JC4 but discovered that it will not work with the brown BMW plug caps, which require a threaded post.
Finally, I called Vech (which, of course, is what I should have done at the beginning) and he is now recommending the Beru version
114Z-4au. I ordered four of these from him and am looking forward to the delivery.