For Campy 144 cranks, one has to barely file down the spider to get the chain to sit right on 41T chainrings. I filed it down at an angle at the bolt surface.

I wonder if some 110 cranks also need a slight modification to get the 33T rings to work. And if 32's are available, they would also likely need the spider to be carved up a bit.

Oh, it looks like Sheldon Brown also sells the 33T rings as singles.

110 mm BCD Mountain and Compact Road Bicycle Chainrings (Chainwheels) from Harris Cyclery