Thanks to everyone who have contacted me so far -- please keep them coming, especially on those closer to the last years, ca 1985.
Although I've got info from some books on some models that were officially sold here in the USA, but I can't seem to find enough on Euro/gray-market versions of these engines, which is what I need. On these Euros, I've received some intriguing bits of info -- but I need more
I'm particularly interested in the:
M110.987 (is this in a '80-85 280SEL/Euro ?) -- horsepower?
M110.990 (possibly in a '77-85 280SL/Euro ?) -- horsepower?

for those also interested, let me share that I've been told:
M110.921 165 hp
M110.984 186 hp and 177 hp (two different opinions)
M110.988 185 hp (also, that the USA version had 142 hp)

Also, I've got figures from that the W126's 280S had 156 hp, while the 280SE/SEL had 185 hp -- but there's no mention of whether these are USA or Euro versions, AND no identification of which versions of M110s these are.

Thanks again everyone.