Slant 6 timing cover
If I recall correctly, the 66 Has a timing tab bolted to the lower driver side cover bolt. I don't remember if the 70 is bolted or welded. he timing marks on the damper correspond to the tab. The 66 bolt on tab can be put on the later cover and just disregard any other tabs on the cover. Depending on the vehicle, the incorrect tab might have to be removed if it interferes with the belt routing.
PS: when maxing/matching timing covers/tabs, and dampers, you can always remark the damper to match the cover/tab being used.