* The truck's owner's manual: This is the most reliable source.
* The vehicle identification number (VIN): A parts website or a dealer can often use the VIN to determine the correct bolt pattern.
* The wheels currently on the truck: The bolt pattern is usually stamped on the wheels themselves. Look closely for numbers like 5x4.5" or 5x5.5" (meaning 5 lug bolts with a 4.5" or 5.5" bolt circle diameter).
* The hub itself: Sometimes the bolt pattern is cast into the hub.
Without more specifics about your 1974 F-100, it's impossible to give a definitive answer.