I just put a pair of 7j 16 et37 rims and a pair of 8j 16 et 30 rims from a 170 slk on my 85 300sd w126. The tires are all 225x55. Everthing fits ok, no rubbing or anything. No spacers. I'm going to put 205x55s on the front and 245x50s on the rear. The only thing not right, yet, is the front little hub caps won't fit because the grease caps stick out to far. The rears use 39mm extended lugs but the fronts stick out farther than the rear so I'll have to find out what fits the front properly. In my searching posts on multiple sites I found some people who said slk would not fit on a 126. I found a lot of people who bought rims because they were told all MBs use the same wheels. I bought mine from such a person. I also drove a long way to a guy who said his 15" rims were off a 350 sdl but when I got there they were et51 which will not fit.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K

I guess for the fronts you may need to use a non-extended bolt. Although I did see 2 different lengths of ~80mm and 90mm total lengths on them. Check yours for overall length.

The front may need a small proper spacer to clear that grease cap, but you know that. It will move that rim out a little which may help track width for the big car.

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'05 E320 CDI
'20 GLE 450