An extra gearbox would certainly be required, and with the stress the gearbox will go through, all metal gears will be needed. The rpm of a wiper motor, although very low, is still far too fast for an electric lifter/flipper. You should be aiming for about 20-40rpm Output after the second gearbox. This would make the arm travel about 120 degrees in about a second.

Windscreen wiper motors vary in speed and torque though, so i cannot say any more.