Way too confusing.
Your fork has a 1" steerer tube.
When you say you have a shim it sounds like your frame is designed for a 1 1/8 steerer and has a 1 1/8 headset installed with reducers for the 1" steerer. This would have to include a special crown race on the fork. I'm surprised that a 20 year old road bike frame would be designed for a 1 1/8 fork.
Are you sure you are not referring to the compression ring on the top bearing?