early manuals list 80-90, later ones (like my '83 manual) list ATF. Regardless, use the same oil you'd use in your diffs. ATF doesn't protect the bearings and gears the same as gear oil, the chart I saw showed a pretty big difference in bearing life between the two.
If ATF gets into the case because of bad seals, it's not the end of the world, but I recommend starting with gear oil.