Adjusting the position of the throwout bearing is not done with shims.
it is done with male and female threads
in the photo below the far right piece is a spacer notched to fit over the input shaft tube mounting bolts.
next is an aluminum piece that slides over the input shaft tube and has full length male threads.
The next piece is the piston assembly and it has matching female threads.
The bearing is a press fit onto the piston assembly snout.
that should give you a better idea of what to expect once you pull things apart
Larry