I have 2 options for fixing my 2.6 190e W201

1st option is a 3.0 from a 300E thats hard to start and didn't run the best but did run probably needs some injectors and other work I just don't know too much about the K-Jet systems. My second concern about the swap from 2.6 to 3.0 is will it pass smog still? California is pretty strict about things.

2nd option I have a 1995 C220 W202 with a M111 engine it runs great with 160k on it but it has all kinds of problems with the engine wiring harness falling apart but it can be fixed. What i'm more worried about is all the extra computer bs that has to be dealt with its my understanding that the computer is tied to the climate control and data is sent to the gauges via RS232. I would ideally like to just swap the whole engine and transmission. Does anyone have experience with this? I have done some research but not found much.
I would prefer the newer engine it would be much easier to maintain once its up and running has standard OBD2 and all that good stuff

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1969 230 inline 6 dual carb 60,000 Miles 2nd Owner doesn't run right
1982 300 SD 455K - my reliable commuter car
1990 190E needs new crank shaft ran it out of oil
1996 C220 bad wiring harness