We did my az race differential in a matter of a few hours at the shop I go to. The hardest part is the snap ring on the end of the tranny. Getting that to line back up is the toughest part, also, when taking the case off, ensuring tht you do not have it tipped over where gears will fall off the lay shafts...
Other than that... it's "easy".
Other than that... it's "easy".