[PJ-Comix]

Who did LBJ nominate to take over Fortas’s seat as Associate Justice when he nominated Fortas to be Chief Justice?

It never got that far. Fortas was not approved for Chief Justice so kept his original seat until bumped OFF the court a few months after LBJ split.

[Publius]

Johnson nominated Homer Throneberry to fill the Fortas vacancy, but the rest of your post is correct. The Senate voted down Fortas, Warren hung on, and Fortas was forced into resignation later due to the Leonard Wolfson affair.