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 B9HS-10 (3626), my first choice, has been superseded to a resistor plug, BR9HS-10 (4551).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 NGK B8HS (5510), which would have been my second choice, has been superseded to resistor version BR
8HS (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.