Buddy of mine had a 292 rebuilt and found this in his gasket set. He asked me what it's for and I'm not sure as I don't remember seeing one myself. Any thoughts? Thanks.

http://s1168.photobucket.com/user/randycox1/media/shim%20010_zpsjmthhaj6.jpg.html

1966 C10 292/tko600 http://67-72chevytrucks.com/vboard/showthread.php?t=596643
1964 C20 292/sm420