Serious Modifications to an EBay Centre Console and slight Mods to shave the plastic edges of the Head Unit to get it to fit between edges of the Console. Took hours and hours of plastic trimming to get nice gaps around the edges.
Problem with trying to leave the BOSE Amp in is that it is not really suitable for anything other than Stock R170 H/U and Speakers, which are old tech.
Even if you just want a simple single DIN H/U Change, you will need to ditch the Stock BOSE Amp, then hard wire the Door Speakers to the new H/U, and also remove the Rear Woofers and put in a pair of Co-Axials or 3 ways or Components .............. 6.5" is really the biggest, although if you wanted to go 3 way then you could likely get a pair of 6x9's in there with a little creativity.
Worth you noting .............
My Car came with a retrofitted Pioneer Single DIN, but had no BOSE and no Rear Speakers from the factory!! The Sound Quality and distortion free outright Volume improved significantly as soon as I installed the Pair of Component Speakers behind the Seats, that was my first move ....................
There is not a lot of room and you cannot cut the Rear Bulkhead for structural reasons and Fuel Tank is banged up hard against it from behind
That is why I have that Surface Mount Sub in between the 2 Seats .............. Does sound amazing tho
I suggest you have a read of my Cars Thread here on SLK Forum, install is a bit disjointed as it was done over about 3 months or more, stages at a time in spare time, but well worth trawling, there is a lot of info in there.
That H/U I used was designed for a W203 C Class, pre facelift model, it was the only one that was physically the almost correct size to fit R170 Console, and I also liked the Knobs and Buttons styling etc as it was a bit more in keeping with an "Old Skool Roadster" like the R170
Thread linky is here, start at Page 2 Post # 30 then keep going, System Install is finished at Page 4 Post # 62 .............
HTH, Cheers Dave