Excellent research and post, Rob. Taking your lead, I went to the Champion spark plug web site
http://www.championsparkplugs.com/ and I typed in the plugs you noted, and that Tom noted.
If you use this site, only type in the numbers, don't put in the name of the manufacturer, such as "Autolite" or "Delco" or any of that.
I ran a couple of the plugs you and Tom noted, and every time the Champion RF10C came up. Therefore this appears to be some good info! Thanks a bunch for the contribution, collaboration like this is great, and it will help a lot of people who have the same questions and needs later!
Regards, Paul