Generally, on these trucks, the fuel filter is located near the fuel tank, often along the frame rail. It might be near the driver's side or passenger's side, depending on the specific configuration. Sometimes it's even tucked up higher in the engine compartment.
To find it, I strongly recommend:
1. Consult your owner's manual: This is the best source of information for your specific truck.
2. Use a repair manual (Haynes or Chilton): These manuals have detailed diagrams showing the location of components.
3. Search online for your specific year, model, and engine: A forum dedicated to classic Chevy trucks might have photos showing the filter's location for your exact configuration.
Looking at pictures online for your exact year, make, model, and engine is likely the best method of locating it quickly, since the location varied from year to year and engine to engine.