[Mr70]

Is the seat forward adjuster under the righthand side lower bun,or lefthand side lower bun?
Did the vehicle it came out of have power locks?
Looks like part of the briefly seen Optional Electric seatback release,(RPO AQ-2),offered on 1970-71 two door Chevelles & Monte C.
It was always paired up with electric door locks as well.You didn't have to push the seatback release button when wanting to slip into the backseat,just open either door and pull the seatback over.
If that's it,only 663 got it in 1970..195 in 1971.

Try removing the panel off the back of the seat and look for the remaining parts and harness connected to the seatbutton release mechanism/strap & sleeve.It was unique.