I am looking for information on Open Element AC Air Cleaners for 1969 Camaro. How can I distinguish between the base for a small block and big block? Is it just the breather tube? Are there any unique markings to identify an original GM part from a reproduction?

Rick's lists same one for 302/396http://www.rickscamaros.com/product.asp?pf_id=EP-116&dept_id=3152

Original bases may have a few wrinkles in the sheet metal caused by the metal stretching when it was stamped. Most reproductions are perfectly smooth.