502 is a GM Performance Parts crate engine, currently, along with the 572 (9.4L). There was a truck application-only 502 available late-'70s thru early-'90s.
The largest displacement "Big Block"-type Chev engine that was assembly-line-available, recently, was the HD 3/4-ton and 1-ton 8.1L (known as the Vortec 8100) which equaled roughly 494 cu. in., an engine size originally conceived in the late-'60s for CanAm road racing.
http://en.wikipedia.org/wiki/Chevrolet_Big-Block_engine