As in one of my photos above with the car on the hoist. Rear adjustment is simple with the sliding plates. You are correct as how they bind when on the ground when adjustment is trying to be made, but when on the correct hoist equipped with the right gear it is way to easy.
And as you said the shim adjustment is the hard part making both sides exactly the same. I used a plum bob and marked and measured 3 known points on each side of the car to dial in the arms. Then got it close enough to original position then drove to the work shop for a 4 wheel alignment.