Yes they well swap out. The pullys must be swaped unless you convert the 240D to the 2 belt setup. If you have a parts car (3.0 turbo) consider doing this. If the alternator belt on the 240D breaks or comes off the car will overheat. The single alternator belt runs the waterpump. In the 300D it is a dual belt setup.
Removing the pulley requires a impact wrench. O'reallys will do it for free I think.


Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car