3.0

the 350SDL had the 3.5


the car "name" usually gives you a clue on the engine displace ment

example

240D =2.4 litre

300D/SD/SDL = 3.0 Liter ( SDL has the om603 6 cylinder where as the D/SD has the 5 cylinder om617)


never heard of a 3.4 liter 6 cylinder diesel..