These are primary resources on the Black Priesthood/Temple ban.
The 1949 First Presidency Statement
The attitude of the Church with reference to Negroes remains as it has always stood. It is not a matter of the declaration of a policy but of direct commandment from the Lord…
The 1969 First Presidency Letter
A 1969 First Presidency letter stated:
Our living prophet, President David O. McKay, has said, “The seeming discrimination by the Church toward the Negro is not something which originated with man; but goes back into the beginning with God…Revelation assures us that this plan antedates man’s mortal existence, extending back to man’s preexistent state.”
The 1964 Stapley-Romney Letter
A letter that George Romney received in 1964 (when Romney was governor of Michigan) from Elder Delbert L. Stapley. Incidentally, in the months after receiving this letter, Romney stepped up his support for civil rights.
The letter indicates that he was including the pamphlet Mormonism and the Negro.
The Lowry Nelson Letters
The Stewart Udall Letters
Additional historical context for the letters: “Do Not Lecture the Brethren”: Stewart L. Udall’s Pro-Civil Rights Stance, 1967.
Dehlin’s summary of facts from 100% Church-friendly Sources
Facts about the LDS Church, Blacks & the Priesthood that Cause Some to Struggle includes many first-hand material from Church-friendly sources.
acknowledgements: Lowry Nelson opinion piece h/t /u/TheLastDarden
Race and the Priesthood Essay - Footnote 9 (Fuzzy_Thoughts)
In August 2020, a Church Historian from the Church History Library responded to my inquiry about the 1949 First Presidency Statement. They wrote:
We can confirm that [The text of the 1949 Statement] was used by the First Presidency in responses to inquiries about the priesthood restriction for several years beginning in 1949. The text was never issued publicly but, rather, was used as standard language in private correspondence.