You can simply rely on the clamping diodes as well to protect the Arduino. Keep the current to <0.5 mA and no problem there.
So an 80V spike on an input, Vcc = 5V, so 75V over. Max current 0.5 mA gives a resistor of at least 15k. If that's the the value of the top resistor of your voltage divider - which normally brings down 14V to 5V, let's make that a 2:1 divider - you're protected from that voltage. Higher is better of course, less current leakage.
The other concern is the input impedance of the ADC pin which is best kept under 10k. It sees the two resistors in parallel. A voltage divider of 20K + 10k would do fine here, giving an input impedance for the ADC of ~6k7 which is comfortably below the 10k recommended maximum.