Interesting...my old w140 S500 had allso 4-web driveshaft flanges while friends 350TD w140 had 3web...that makes me think that SL500 should allso have 4web...but I hope you are right.
Anyway why are yu bothering with meqasquirt 12cyl cop ignition? I am no pro. on this subject but seems to me that meqa can only handle up to 8cyl cop or 16cyl wasted spark? IMo it would be easyer to use VEMS or smth like that...price is the same as meqa, put its sure that this ecu can handle`em...

regards,

Allar