To address the initial question:

1) The 123 source vehicle was produced between 1977 & 1980.
2) The transmission is a 722.1xx.
3) The transmission in the 460 is a 720.1xx
4) Between the engine and the tail housing the two transmissions are externally the same.
5) If the tail housings/output shafts/output flanges are the same, then the sedan transmission is a bolt-in.

To answer the question a picture of a 460 722.1xx transmission is required.