Whoa! Installing a ring-n-pinion is an artform. Nothing less. It can be the difference between the set lasting 30K or indefinitely. If you have never done this, as I suspect, you need to get some assistance before you go any further. I have seen this done but have never performed it myself.
Is this gearset new? Have you pressed the new pinion bearing races in the axle housing yet? New pinion crush sleeve?
Do a search on the subject. :book1: Getting it right takes time & patience. Even pro's assemble & dis-assemble it many times to get it right.
GT