A limit of ten years is mentioned nowhere in the Constitution.
If Ford appeared electable, he would be nominated. Otherwise he wouldn't.
The 22nd Amendment states "No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of the President more than once." This would seem to allow Ford to run for president in 1984 since he had never been
elected president before. (He had been appointed vice-president in 1973 and then succeeded to the presidency in 1974; he had been elected
vice-president in 1980 and then succeeded to the presidency in 1981.) However, if elected he would not be eligible to run again in 1988, since he had served more than two years of Nixon's term (and more than two years of Reagan's) and been elected president in 1984. At least so I argued at
https://www.alternatehistory.com/forum/threads/fords-third-term.425983/ though evidently not everyone shares my interpretation...
I agree that there is no ten year limit. If Ford had become president in mid-1973 instead of August 1974 (both the Agnew scandal and Watergate reach a denouement quicker than in OTL) and president again in say February 1981 (Reagan is fatally shot not longer after his inauguration), Ford can still be elected in 1984 even though at the end of his term he will have served close to twelve years of office when his term ends in January 1989.