First, the dist cap on a 1990 300E will definitely come off without removing the fan! I've taken the dist cap off first every time I"ve removed the fan on my '91 300TE 4m.
Second, the fan is actually very easy to remove with the clutch once you fab the tool. The manual describes the tool and it is made of 3/16" rod, very similar to the heavier coat hangers one might find at one's office. There is a 90 degree bend at the end that catches in a hole in the back of the fan clutch to hold it tight while turning the 5 mm allen bolt in front. Once you get the allen bolt to bust loose, you're there!
Check out the manual for the tool, they are sold by the tool companies for $15 - $20, but it's the easiest tool I ever made.