You can jump a 6v vehicle from 12v battery. Just don't crank the starter too long.
Also, how often have you ever needed a jump start on any vehicle? If you're like most of us with old cars, you are intimately aware of every aspect of your vehicles' conditions and states of repair and likely aren't caught off guard by a dead battery.
I'm usually the one giving people jump starts in the parking lot or side of the road. I can't even remember if I ever needed a jump start in the last 25 years or so.
Remember also that you're driving a stick shift. Roll starting these trucks is pretty easy.
