If you do have to remove the cup, a good trick is to pack washers against the spanner for the fixed cup and slightly tighten the crank bolt against it, so that when you're removing it, the spanner doesn't slip off. As it's a very thin spanner and the flats on the cup are thin, you'll probably have to fix the spanner there after several goes and bruised knuckles!
Campag made two tools for this. One was a standard very thin one and one was a big fat workshop one costing a fortune. The spanner is shaped the same as the cup with a 36mm spacing across the flats.
Old enough to know better!