I've found a set of 2010 S550 18x8 4 matic rims. Will they fit an 2002 E 320 4 Matic. Is the Back Spacing similar?
Not sure which wheels your referencing, but looking at the list published on alloywheelsdirect shows they may be close enough to work.
But why guess, ask what the actual numbers are on the back of the wheels you have found. All AMG-mercedes wheels have the sizes either cast or stamped into the back of the wheel, (usually).
Look for 3 numbers grouped together, (8Jx18H2et43 for example).
Also look on the wheels on your car and get their numbers.
Post back what the answers are.
Even if the offsets are close enough, (I think they will be), you still may have the lug bolt size problem.
I can't find it offhand, but I read somewhere that the lug bolts for the new S class are 14m with a R14 radius ball seat. The lugs on your car should be the older 12m size with a R12 radius ball seat.
So if this is true, you will need a lug bolt that will screw into your hubs, (12M), and a ball seat that will fit the wheels, (R14 radius). Then you need to make sure the length of the lug bolts are long enough to be safe, and short enough not to make contact with brake components.
These strange lug bolts are available here
Look in the ballseat lugbolt section and you will find two offering with the thread and ballseat sizes you need, but they are different lengths, 26mm and 35mm. They also sell a 12M x 40mm R13 bolt that may fit as well, if you need a longer bolt than 35mm.
You should call them and explain what your intensions are, they have a great working knowledge of wheels and bolts and will be able to recomend the right bolt for your application.
I know because I put SL55 wheels (22 spoke Turbine uses 14M R14 bolts), on a SL that normally uses 12M R12 bolts. RADUSADIRECT had the exact bolt I needed, and they bolted up perfectly.
PS: just got to thinking about the wheel width, even with the ET's being close, be careful you don't go too wide, 8 inch may be at the top end of the width allowable depending upon ET and tire width.
You should also go to the W210 forum and ask these questions, I'm sure someone there has tried just about everything, and they will know what will rub and what won't. good luck