Hi!
If you take in a Kompressor engine you would have to get everything from a halfcut and most probably the differentials as well as every bit of parts work together. Which Kompressor engine are you interested in? The ones from the latest C class are 1.8s. Therefore am guessing the E class 200 kompressor with the round lights? In terms of mountings there should not be a problem but, as mentioned, you would need to get the whole half cut system, the differentials plus a good mech. In terms of cost, I never asked what's the cost like though on these half cuts but if you do find out let us know! It would be great to see a 124 with the Kompressor engines, if you don't go for those you would think of the E230 engines, they're great too. Smooth because I used to drive a W210 E230. Awesome car.
If you want an engine without any change in wiring, you could think about the 300E engine. The thing is to not change any wiring you'd have to use the same type of engine like the 300E or the same 260E engine. For the 230E I am not sure but most probably you might since the fuel relay and stuff could be different, but have to check first. Anything new or very different you will have to change the wiring.
