This is a tough one. Ford never had much ambition to be President as far as anyone knows. I suppose the best chance is elevation to the Presidency during the 2 years he was Speaker, but that would involve a most unlikely event -- the deaths of both President McGovern and Vice President Hart sometime between 1983 and 1985. That's unlikely as Hart is still alive and McGovern just passed last year.
OOC: In this TL, Agnew never resigns because his tax evasion is covered up and Nixon's involvement in Watergate isn't exposed until after he leaves office at the end of his full second term. Reagan wins in 1976 and takes the fall for a bad economy and Iran, turning the country sharply to the left. A poor economy and a McGovern proposal for universal health care leads to a 1994ish midterm where the GOP wins the House over a slow recovery and a seemingly radical UHC proposal. Once the economy picks up steam in 1983/84, Democrats get back the House and McGovern/Hart win in '84.