Here are the most likely scenarios:
* Under the rear bumper: Many 1950s cars, including many 210s, had the fuel filler located under a small door or panel on the rear bumper. This door would typically have a latch, handle, or knob that needed to be released to open. Look closely at the rear bumper for a small, often recessed, handle or button.
* External release inside the car: Some models might have had an internal release mechanism, possibly a small lever or knob located somewhere within the car's interior (potentially near the dash or under the steering column). Check for anything that looks like a fuel filler door release.
* Combination Lock: Less common, but some owners added aftermarket locking mechanisms to the fuel filler door. This would require a key.
Before attempting to open it:
* Inspect carefully: Look for any visible latches, handles, or markings around the potential location of the gas cap.
* Consult a repair manual: A repair manual specific to a 1956 Chevrolet 210 will be your best source of information on the location and operation of the fuel filler door. These are available online and from automotive parts suppliers.
* Check online resources: Searching for "1956 Chevy 210 gas cap location" or similar phrases may reveal photos or videos showing the mechanism on similar models.
Remember to be gentle to avoid breaking anything. If you're unsure, it's best to consult someone experienced with classic car restoration or a knowledgeable mechanic.