It's hard to recognize in pictures, and even in person, but the 355 is a much smaller car than the 360. It's 11 inches shorter! It's also 200 pounds ligher, dispite the move to an aluminum structure in the 360.
http://upload.wikimedia.org/wikipedia/commons/1/18/F355_Berlinetta_in_Taipei.jpg
It's 4 inches shorter, 4 inches lower, and 4 inches wider than the 986. With a wheelbase of 1 inch longer.