interfacing controller to pedal

here is a controller for a pmdc motor



now does anyone know how this can be interfaced to a lever via a potentiometer.

my idea is that the lever is mechanically attached to a potentiometer, which in turn is interfaced to the motor via the cables.

the linear movement of the lever adjusts the potentiometer , which in turn gives the signals to the controller to vary the motor speed.

now what i want to know is , what would the potentiometer look like and how to do the interfacings ?