[63sbssbbw]

Your old box:
It's hooped,so tear into it!,see how it works
The nut and allen bolt adjust gear lash (this lash setting is established at the factory or reman using in lbs/ft resistance btween output and input)
Inside should be 24 ball bearings 12 dark and 12 shiny ones,they are 1 thou different in size.
if your careful you may be able to determine if they were installed correctly(alternating 1 big 1 little 1 big and so on)and that ALL 24 were installed
I have heard of 1 bb getting lost and it being reassembled anyways with the result being a very scary dead spot like your experiencing.
Your new box:
pretty basic,follow CaptFabs instructions.
As Padresag stated,wheels up.
There are threads discussing ps boxes in detail.
But there's nothing better than tearing the heck out of something knowing that you don't have to put it back together,just to see"how it works"
T