In Mormon Doctrine page 575, Elder McConkie states “the plan of salvation was ordained by the Father. It is not the plan of Christ…” In The Encyclopedia of Mormonism Gerald Lund states the same: “The Father is the author of the Plan of Salvation; Jesus Christ is its chief advocate; the Holy Spirit helps carry it out…” However, in the Pearl of Great Price Student Manual Religion 327, Elder Talmage is quoted“…the plan of salvation, the author of which is Jesus Christ…” Who authored the Plan? Father or Christ?
When we review the teachings from lds.org we are able to read the following statements provided:
1) The Father — “God is the Supreme Being in whom we believe and whom we worship. He is all-powerful and all-knowing, and He is full of love, mercy, charity, and compassion. He is the Author of the plan for our happiness.”
2) Abraham 3:27-28, “I will send the first.” God our Father presented his plan. He revealed who would be the Savior.
3) Joseph F. Smith, “Our Heavenly Father designed the plan of salvation so that we can be exalted.”
4) Pearl of Great Price, Religion 327 Manual, “To ‘keep’ this first estate, a spirit child of God in pre-earth life had to use his agency to choose to follow the plan of salvation offered by Heavenly Father.
5) Pearl of Great Price, Religion 327 Manual, “Adam, the patriarch of the race, rejoiced in the assurance of the Savior’s appointed ministry, through the acceptance of which, he, the transgressor, might gain redemption. Brief mention of the plan of salvation, the author of which is Jesus Christ, appears in the promise given of God following the fall…” (emphasis pointing to your question’s origin)
James E. Talmage’s quote, referencing Jesus Christ as the author of the plan of salvation, is in the same light within Elder Dallin H. Oaks testimony,
“I testify to you, my beloved brothers and sisters, that these words are true, that this message is the doctrine of Jesus Christ, the plan of God our Eternal Father, of which our Savior, Jesus Christ, is the author and finisher.”
Elder McConkie suggested reading of Hebrews 12:2 (where we get the phrase “author and finisher”) as “The Leader and Perfector of our faith. In Heb 2:10 the word for author is translated captain. It is the Father, not the Son, who is the author in the sense of originator. The gospel originated with God; it is his plan of salvation which we and Christ accepted in the pre-existence” (Doctrinal New Testament Commentary, vol. 3:222). If you would like more information, here’s the concordance for archegos (“author”, “Prince”, “captain”).
The plan originates with the Father. Jesus Christ is the author and finisher of our faith, which I would say is highlighted in the full quote that contains the quote you have given by James E. Talmage.