if you are just setting up preload you shouldn't need a press. just a vice to hold the bulk head a good torque wrench and a preload gauge. If you put shims behind the bearing you will be adjusting the pinion depth not the preload. I would say pick one torque it down check the preload then you will know whether you need a thicker of thinner shim. Thats the wonderfull world of building diffs sometimes you get it on the first shot and some times it takes multiple times.
