I've been looking at this as well...
I've got a W208 320.
I've read about a guy in the USA who fitted the 3.7 to his 3.2 Chrysler Crossfire, which is a Mercedes SLK in a different Dress.
Physically it fits no real bother at all.
The 3.7 m112 and 3.2 m112 use all the same sensors on the engine.
The V6 Bolt pattern to the 722.6 gearbox is good
The 320 Ancillaries are used AC, Alt, Pow Steering, Water pump
The issue is Security and compatibility when swapping over Mercedes ECU's.
I've asked a tuning firm about resetting my cars ECU to allow for the increased displacement and have not had promising answers.
A Few places offer to reset a used ECU and clone your cars security settings to it, but not got any definite leads yet.
If the ECU is from same family/version it should work
There is the issue of the supporting systems such as Transmission Control units and other black boxes which are matched to the running gear of your W202. That could be a stumbling block.
However I am now exploring the idea that the car, well my 320 at least is capable of adjusting the tune itself via Lambda info.
Eg use the 3.2 V6 ECU and loom on the 3.7 Engine.
The Sensors are all the same (I've cross referenced them, except for a cam sensor which is Early or late on both engines)
The injectors are matched and of the same type and impedance (e.g "sized" bigger to suit 3.7)
The car won't know it's now a 3.7 or that it has bigger injectors and will just aim to keep the correct value based on Lambda info...
I would plan to use as much standard parts as poss and then have an exhaust made up to from CAT back to suit diameter of 3.7 pipe work
If anyone reads this and knows of someone able to write a file for Mercedes ECU or what can be swapped to make it work I'd be interested to talk to them
These engines reportedly can go to 280BHP once remapped!
300BHP must be possible with a Camshaft swap and free flowing exhaust
This would make my old CLK have C43 power with shorter final drive gearing and 100KG less
The initial swap makes some sense if kept simple... Tuning it...not so much...
hth
