You will have to look in the Chevy Parts catalog:
This catalog can be used to find a part number (which is pretty much useless since they are all obsolete), but can confirm or identify a part (almost all parts were stamped with a part number for inventory control, but some where boxed or paged which disappeared on the assembly line, or they had an adhesive tag that fell off years ago. Catalog had exploded views of some group items which helps to identify not only a part in box but where it goes in the car.
With the catalog (a pdf document) you can search for a part number to see where else it appeared (model and year). This will give you a clue as to whether the part is still being made and sold as a reproduction part (like on a light truck, or a Corvette that isn't listed in an Impala web site).