That chart is incorrect.

'66-'69 Dana 60 rears used (heavy duty 4 pinion) 23 spline Power-Lock sure-grips.

'70 Dana 60 rears used (heavy duty 4 pinion) 35 spline Power-Lock sure-grips.

'71-72 Dana 60 rears used (light duty 2 pinion) 35 spline Track-Lock sure-grips.

The date is Sept 16, 1970