Boeing 767-300 does not have individual video screen at each seat. Nowadays, there are only the B-777 and AIRBUS 340-300 that have individual screen configuration.
You can call American Airlines 1-800-443-7300 to select your preferred seat a month before your departure day.
According to my experience, ask them for the seat at one of the following rows : B, C, E, F ... for they are the most comfortable rows for the long routing.
Where will you fly to and from where ? Have a good flight.