To be certain, I recommend:
1. Checking your owner's manual: If you have it, this is the best resource.
2. Looking near the battery: This is the most common area for starter relays.
3. Consulting a wiring diagram: A wiring diagram specific to your year and model will show the relay's location precisely. You can often find these online through resources like Haynes or Chilton repair manuals, or possibly even on forums dedicated to classic Chevrolets.
4. Visually inspecting for a relay that's likely connected to heavy-gauge wiring: Starter relays handle significant current, so the wires connected to them will be thicker than those for other relays.
Remember to disconnect the negative battery terminal before working on any electrical components.