1970 Duster base model slant 6 rear differential 2070051 spider kit

All 65 to 72 a body’s had factory 4 inch bolt circle, even the 8-3/4 axle. It’s probable that someone had swapped a late model rear into the duster you had gotten the rear axle from, though. I had to do that on my first ‘71, I got the donor from a ‘74 valiant four door with disc brakes on the front. It was a six cylinder car and had wider drums on the back, but I don’t remember the diameter. But it was still a nine bolt cover. The outside stud width and spring pad widths were identical.