Re: Spare Tire
If the spare wheel fits on the front, no worries about the rear. A lot more stuff going on behind those front wheels than the rears.
Although, if the bolts you use to mount the spare are too long, I think you might run into interference for those bolts faster on the rear. So make sure you pay attention to the bolt length and the seat shape (ball shape, not a cone like many others). With luck the parts yard might have the handy clear plastic bubble holder which the Mercedes shorter lug bolts were originally packaged in with the temp spare wheel when the car was new.
Good luck! And would you please come back and report what you learn? Particularly if you discover a different Mercedes spare works. With that please note that many used part sellers have listed these spare wheels as having the part number from one of the warning labels on the wheel, which cautions about using only the shorter lug bolts. The big number on that label is only for the label, not the wheel. So tell us the part number for the wheel - cast into the back.