Build Date N54 - N55 Swapover BMW 335is

What was cut off date for the N54 engine in the 3 series etc

I am looking at this exact car

http://www.carfax.com/VehicleHistory...&partner=ATD_W

http://www.autotrader.com/cars-for-s...gIndex=2&Log=0

Dealer cannot tell me if it is N54 or N55 (open the $#@!ing engine I say but they are dolts) and I am not driving all the way down there if it is N55