Remove the three bolts at the bottom of the lower bearing plate, remove the shim plate and turn the lower bearing plate 180 degrees. Now you can pivot the yoke up and down. Remove shims evenly from both caps until you feel drag when pivoting the yoke up and down.
You will probably find one or more problems when doing this job. First the bottom plate will probably fall out of the lower bearing. The shaft will probably be worn which will allow play in the wobble drive.
The second problem you will find, if you are not replacing the bearings, is when you remove shims and you rotate the yoke there will be tight and loose spots in the arc. The side bearings and cups get beat out and the surfaces are like corduroy.
If there is ANY play in the rear mounting bearings on the main shaft, remove the wobble drive and rebuild.