I have an early 8-3/4, need info on

Casting numbers 2070742 (used from 1961-1969) and 1634985 (used from 1957-1964) identify the 1 3/4-inch-diameter 10-spline pinion shaft, and are commonly referred to as the "742" case.

Casting numbers 2070741 (1964-1972) and 1820657 (1957-1964) identify the smaller 1 3/8th-inch-diameter, 10-spline pinion shaft, and are often called the "741" case.

Casting numbers 2881488 and 2881489 were used from 1969 through 1974 and were the only cases used after 1973. This is the most sought-after 8 3/4-inch version, and is called the "489" case. The pinion shaft diameter on these rear ends was 1 7/8 inches, and these pinion shafts were either 10- or 29-spline.

From this website
https://www.hemmings.com/stories/article/mopar-8-3-4-inch-rear-ends