new pinion and output seals. Help!

[72blazerblue]

I plan on replacing both pinion and both output seals. But i am pretty worried about two things:
1. How tight do I get the nuts on pinion/outputs? Some say mark where it is now and put itt back there, others say torque it. I'm really worried about over or under tightening it... Which do i do??

2. When I put the seals in, how do i know how far to hammer them in?
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