AFAIK the engine bay of a W201 is the same regardless of whether it housed a 4cyl or 6 cyl. But I could be mistaken. What I DO know is that someone transplanted a C36 engine into a 16v. Took a lot of time, money and effort, but it was a successful swap.

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'94 W124.036 249/040 leder; 8.25x17 EvoIIs
'93 W124.036 199/040 leder; 8.25x17 EvoIIs, up in flames...LITERALLY!
'93 W124.036 481/040 leder; euro delivery; 8.25x17 EvoIIs
'88 R107.048 441/409 leder; Euro lights
'87 W201.034 199/040 leder; Euro lights; EvoII brakes; 8x16 EvoIs - soon: 500E rear brakes
'70 R113.044 050/526; factory alloys; Euro lights