First of all, thank you all for your help. There is a wealth of practical experience with the folks on this website. I had an opportunity to get to the boat this weekend. As it turns out, the old plugs are surface gap NGK BU8H. That is also the plug that is listed for my outboard (1980 Mercury 200 HP) on the Mercury 2016 US Accessories Guide...Mercury part number 33-13686Q. So, that is what I purchased today.
The engine runs well at cruising speeds, but idles rough and stalls. Hopefully a fouled plug is the cause (?). I will find out in the next week or two.
Thanks Duke
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