you don't need to pull the cover. unless you want to. i think i run 75-90 in my rear axle? not sure, i just buy w/e.. if you have a LS you need to get the additive too.
edit: what he said.. i forgot, higher end stuff like lucas too dont require the additive.
just take the bolts out, place the diff guard in place and put the new or origional bolts back in.