WI: Martin Van Buren lives to 1879?

This year Jimmy Carter turns 97, this has led me to begin a series of threads on what if every President had lived to such an age. As it's been a while since the Millard Fillmore discussion, here is the second: What if Martin Van Buren lived to age 97 (1879)?

As it is, Van Buren died shortly prior to turning 80 in 1862, in the midst of the Civil War and a year after rejecting offers to host a meeting of former Presidents in an attempt to prevent secession. Despite his initial (i.e. 1820s) support for Black suffrage and later (i.e. 1848) Free Soil advocacy, Van Buren was a strong supporter of the Dred Scott decision and related policies at his death.

Does he continue in this vein and support a mild, Johnsonian Reconstruction? Or, in typical Little Magician fashion, have yet another change of heart? I am guessing his Democratic views and friendship with the latter two ensure that supports McLellan, Tilden, and Seymour, might he support Grant over Horace Greeley? As it is he never finished his autobiography, leaving us with an unedited, tedious work that spans hundreds of pages yet does not extend pass the 1820s, if he completes this how might it effect perception of him?