No, that piece is used for all of 70. It changed in 71 when I dont think anything was used there? There is nothing shown in 71 Assembly manual. I don’t think my 71 had it. I will take your word on 69. Shown is 70 assembly.
I just parted out a 69 with the ST300 trans, and it had it also. It also had the electric kick down switch/bracket and the no-cable type gas pedal arm that was used on the TH400 cars. The little plastic square-hole plug in the firewall was also there.
It was used on all 70 engine/transmission combinations. My 70 GSX 4 speed had it. All cars have a throttle cable and that what goes through it. 455 cars had the square plug as well as that piece.