"But:
When starting, you sometimes get a fair amount of black smoke (exhaust pipe). I am sure the valve seal leaks a little but this does not smell of oil. Also, for about a block, if you press the accelerator hard (not slamming it but just pressing it), the car bucks and you get a big cloud of black smoke. After a block, no problems, car runs great."

You do not specify whether this is a hot or cold starting problem. If cold, then re-check your cold start valve to see whether fuel might dribble out after the start period. As I recall, these are supposed to shoot fuel for about 10 seconds to aide cold starts, then stop. They operate only below certain temps. If it continues to run fuel, check your time switch, too. There are several temp sensors involved (air, coolant) so check the book for testing values (resistance at certain temps) and run through each of them to ensure proper functioning.

FYI, my 350SL 4.5 is also a bit rough at idle when cold, but runs fine otherwise. I just chalk it up to age (like my wife does with me).

Your tan plug color is a sign of a perfect mixture setting for when the engine is warmed and operating normal. You won't get great gas mileage, but the power will be excellent. Be happy...

230/8