Read on a couple pages, take it as you will:

1958-1969 used the Dana Power-Lok (# 2881487)
1969-1974 used the Borg Warner Spin Resistant (# 2881343)

(Source: 1984 Direct Connection Chassis Book)
9 ¾ AKA Dana 60
The early rear ends were 23 tooth "Power Lok" (1966 - 1969) differentials. In 1970 the 9 ¾ went to 35 tooth axle shafts and were called "Track Lok" differentials.
Dana Power Lok, 1962 - 1969 which are rebuildable (clutch packs)
Borg-Warner Spin Resistant, Late 1969 - 1974 which are not rebuildable (cone type)