Back in the days when there were many more Seventies spread throughout the Church (146 quorums in 1904!), B. H. Roberts of History of the Church fame wrote five years of manuals for quorum meetings, collectively the Seventy’s Course in Theology. First published 1907-1912, they are now available on Project Gutenberg for your reading pleasure.
The manuals are broken out into lessons, most beginning with an outline and references, followed by a series of notes. Many of the notes are quotations from other commentators or Roberts’ other work.
It seems clear that Roberts wanted to radically improve his typical student’s intellectual stature, and that’s inspiring to see in action. In one lesson, he identifies the works of thirteen different philosophers as references, and since those works may “only be available to those within reach of reference libraries,” he also recommends eight “one-volume works that would be of great service in studying this lesson.” In several locations he comments of his lesson notes that “They make difficult reading, but—well, master them.”
Each year has an overarching topic, as follows:
Year 1 – Outline History of the Seventy and a Survey of the Books of Holy Scripture
Year 2 – Outline History of the Dispensations of the Gospel
Year 3 – The Doctrine of Deity
Year 5 – Divine Immanence and the Holy Ghost
I’d suggest starting with the topic that is the most interesting to you rather than reading in sequence, as the different years don’t seem particularly cumulative. Year 3 seems to have some overlap with Mormon Doctrine of Deity.
Thanks to Renah Holmes for proofing two volumes, and BYU Transcribe as coordinated by Rachel Helps for proofing the other three!