The following is a pretty useful essay on the ages of the patriarchs in the JST:
Kent P. Jackson and Charles Swift, “The Ages of the Patriarchs in the Joseph Smith Translation,” in A Witness for the Restoration: Essays in Honor of Robert J. Matthews, ed. Kent P. Jackson and Andrew C. Skinner (Provo, Utah: Religious Studies Center, Brigham Young University, 2007), 1–11 (PDF)
