chevy 350 heads

Hi all. I have a set of heads that were supposed to come out of a ' 76 vette. I have some numbers and I am not sure what they all mean. Can anyone help me out here. On both heads there is a 333882 number. There are more numbers but they are not the same on both heads. One head has a GM 21 and C4 6. While the other head has a GM 31 and L 235. If anyone could help me out I would appreciate it. Thanks.
duckenit

Regular old 74-80 350/400 open chamber 76cc heads.

I found this info at http://www.mortec.com/castnum.htm and you can to. Bookmark?

Thanks for the help. I know what the 333882 numbers are. What I am looking for , is what the other numbers mean. If you can help me there that would be great. Thanks. :D