Another Rear Question.. Well two.. but easy ones!

[ShortBedChevy]

Ok, two more questions... I can repair my rear end for $30... I need to replace two spider gears in the posi unit... I have the little bolt that holds that big bar off, the two spider gears go on the bar, but i can't seem to get the bar to come all the way it, its moves a bit now, but wont come out, any suggestions?

here is a picture, you can see the bar.. .the two spider gears are gone, as they blew apart also the two "washers"? that go on the outside of them... but everything else is perfect...


here is basically what i need minus the two side gears...



Also, when i am all done.. I know this is stupid... But how exactly do i fill the rear end back up with oil?
Thanks guys and gals....