Williams Daniels reprises his role as "John Adams" from 1776 after portraying his own cousin ("Samuel Adams") in the previous miniseries THE BASTARD, making him the only actor to play both Adamses.
The miniseries rewrites a lot of material concerning the two main characters. It has Philip Kent and Judson Fletcher interact quite often. In the book, their stories are completely separate. They never meet.
Other than William Daniels playing another Adams, Tom Bosley as Ben Franklin seems to be the only other actor to reprise his role from THE BASTARD.