Take the fan off. I've done them both ways, and it's MUCH faster to pull the visco clutch -- one bolt and some way to hold the clutch (the 300D has a slot for a piece of 1/8" wire or a 4mm allen to slip into the clutch).
Beats the dickens out of wrestling the belt around the pulleys with the fan on. Take far less time, too.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!