1970 Duster base model slant 6 rear differential 2070051 spider kit

Joel, If this is a non sure (open) grip rear. The parts you need are spider (pinion) gear part number 2404 195
Also recommend axle end gears part number 2404 194
This vender list the parts in stock
Brad Nos Parts Westcolumbia Chrysler
(803) 755-0066
https://bradsnosparts.com
If a sure grip rear, lots of luck.