Run it over 50 at great risk. These old trucks didn't have a lot of horsepower so they were geared low to compensate. You can get lower ratio gear sets but they're expensive. As red58 said, your dad is dreaming.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.