Let's start with basics. Engine compartments are the same dimensions on all W201's. The 2.6 litre inline six of the 190 2.6 is the same block as a 3.0 litre. It can't possibly be that hard, placement-wise, which is not to minimize other challenges.

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Charles Cleaver
1975 350SE + 1992 300CE-24 SportLine 5-speed + 2002 SLK320 6-speed + 1974 W114 280
1986 190E 2.3-16 (Decomm rear self-leveling suspension; Euro-code headlamps) sold
2004 Audi S4 6-spd - sold
1969 (2) and 1980 Porsche 911T, S, and SC - alas gone
1987 300SDL - Graf Spee; Euro-code headlamps; 16-inch 8-hole wheels - sold
1994 E420+(E500 suspension/E-code headlamps/PAD chip) sold
1968 250SE 4-speed (NICE car) - long gone
1962 220S 4-speed/column mount - long gone