You remove one of the smaller cone or Belleville washers and use all 3 of the larger ones. Unless you are wanting to make your diff very tight, this isn't the best way to do it. This is a technique that we used many years ago, but abandoned cause it seems to load up the thrust washer unduly and causes premature failure. A diff built this way is never "smooth" and needs frequent rebuilds. If I remember correctly, leaving out one of the large washers gives you a looser diff.

What might be a better way is to build per the instructions, but use a shim or shims on the diff nut or screw. It takes the same size shim as you use on the axles. The advantage here is that you can make the adjustments in 0.1mm increments so that you can have the diff action you want. I generally use between 0.2-0.5mm in shims, but I do't run them ultra tight.

With stock internals and a 20t pinion the 03, 05 and 06 all have a 5.8fdr. The internals are all the same. 04 internals are the same, but the motor mount holes are offset differently, so it uses odd numbered pinions, like a 21t.

Or were you asking if they allow cheater gears?