Strato seat back on 69 nova

[Mr70]

You need to remove that plastic chrome lock button first.
It has spring clips on the side that hold it very securely,so it can be a challenge to remove w/o destroying.
They usually break in pieces if old & brittle and guys buy new shiny ones anyway.
I used a homemade tool out of a hacksaw blade ground down and wrapped with cloth tape to better grip it with.You need a tool that flexes as opposed to too rigid.
You have to "walk" the chrome button out,one side a little,then the other side a little,then once out,it gives you access to remove the 2 bolts hiding behind it holding the seat back on right there.

Pic showing spring clip locations behind it.