Recently a game was played where two GMs swapped kingside and queenside knights and then agreed a draw (and got their just dessert): How often can the starting position be repeated in a game without automatic draw? Since even four castling rights can be forfeited, the answer surely is "75 moves".

EDITED OUT: The not 100% FIDE-compliant, but mathematical more interesting question is that you assume automatic draw on repetition but NOT on 75 moves without pawn move or capture, and no player claims. This will be a very large number, in the order of (32 over 4).