so no markings at all on either the fixed or adj. cup?
Do you have a regular British (ISO/BSC) adj. cup you can try in the shell?
I wouldn't try a Crescent wrench (of any size) on a fixed cup, my knuckles ache just thinking of it
You want a fixed cup wrench, the big-bolt-and-stack-of-washers to hold it on tight...and maybe a dead-blow mallet (or just a BF hammer) to knock it loose...in the right direction, of course.
Your knuckles will thank you!