Hi JohnS, what you have found is the excellent M100 site that caters for all Mercedes models with the M100 engine, such as 600, 6.3 and 6.9's.
Several members of TOPKLASSE are in fact members and subscribers of and to the M100 Register. Some that come to mind are S-Class, abl567, WGB and yours truly.
What some may not know, the M100 Club, through the untiring and enthusiastic efforts of Dr. Arthur Love in Brisbane, is coming to Australia for an Australia Wide rally in the later part of September of this year. That should be quite an event, and I will be taking part in it in some sections, say Sydney-Melbourne, or Sydney Brisbane. Regards Styria