Hi Harold and a warm welcome
The little brass gear that sits on the outside of the plate is a tight fit on the steel arbor. If you can, find a way to hold the little brass gear and punch the arbor through it. You can get what is called a brass split stake but in this instance I dont thing you would be able to use it. If the wear is not terribly bad in the pivot hole you can just clean it out as best you can without taking that arbor out. Just remember to oil it when the clock goes back together. The other problem you might encounter when putting the mech back together is restraining the main spring. I always found zip ties or cable ties helped with this.
Good luck Harold and let us know how it goes and if we can be of any more help