I can get my hands on all 4 wheels from a Slk320 2003 for 17x8 rear an 17x7.5 , pretty sure the rears fit I race on 16s on tje rear but wondering would the 17s clear the rotors

 

Those sizes sound more like a R171 than a R170, R170s (SLK320) came with 16s. Do they look like this ?

 

I've got 16" R170 wheels on mine for the winter and it clears the front rotors. 17" ones shouldn't be an issue. Mine look like these:
http://img.retro-rides.org/i/v/negat...915ec6abe4.jpg

 

That looks like the sport option. Standard wheels are five spoke. Ae they 16x7 front and 16x8 rear ?

 

1997 SLK 32 GOT 17s wider 17x8.5 rear pretty nice wheel

 

Sorry, my wheels aren't like the picture I referenced earlier. See attached pic for the actual wheels on my car. I'm not sure what year SLK they're from or the width. But they're 16" and they clear the front brakes.

When I was buying those wheels I tried searching for whether 16" wheels would fit the car and I couldn't find a conclusive answer, so I actually test-fit them on before buying them. Hopefully this will help someone else. The rears are a bit "sunken in" compared to the stock wheels, but it's fine for winter and doesn't look too out of place. The only thing I had to do was get shorter bolts for the rear wheels (I got original SLK bolts) as the Crossfire bolts were too long with these wheels, went in too deep, and were interfering with the parking brake mechanism.

 

Puts it down there... Get a set of spacers, then you can put those rears out a bit..imho.