Quite rare in 67. Most but not all convertibles got them. Some were ordered with only 1 headrest. These headrests were actually borrowed/transplanted from B-body buckets. The oval headrests for 68 and later are much more common in A-body and others.
The original skins may still be beneath those tan covers. I don't know if some place like Just Dashes could/would restore the OEM skins.