To be absolutely certain, you should:
* Consult your owner's manual: This is the best source of information for your specific vehicle.
* Check a repair manual (like a Haynes or Chilton): These manuals contain diagrams and detailed instructions.
* Look online for diagrams: Search for "1987 Chevy Astro 4.3L fuel filter location" on image search engines like Google Images. You'll likely find pictures from other owners that can help you identify it.
Remember to be careful when working near fuel lines and always follow safety precautions when dealing with fuel.