Can a vw beetle engine be put in a porsche 911?
 

You are talking trying to fit a 4 cylinder in place of a 6 cylinder Mb Star C4? That leaves room for cases of beer. Also you would sound like a V.W. 4 cylinder. You can't hide that sound.
People put V8's in there though the radiator set up is quite complex. And the car does not handle worth sht.

If you can get a Mb Star Connect C4 Porsche without an engine, then you can get an engine without a Porsche probably easier as the bodies get wrecked before the engine blows apart.
Why not get a 65 Chevrolet Corvair engine which is a 6 cylinder air cooled engine and put that in? It is matching it up to the transaxle where the challenge is.

Life is too short to mess around with something that will not pass emissions.