I would do the diff as well as everything else, the rebuild kits are like $70-$80 and since yours doing the gears, might as well do that too, you will be happy that you did, trust me
I have 2 NOS blue nitrous bottles, both are 10lb bottles, one older and one brand new, both bottles in good condition and also have a dual billett bottle holder for them, dont need them any more, someone come get them.
$500 or BO