How many different casting numbers are there for aluminum BBC heads?

[AnthonyS]

Thanks for the discussion everyone, I'm really not sure what I have here then.

I've got a pair of match dated 05-27-68 square port aluminum heads that I can't find any info on, even https://www.mortec.com/bbc.htm doesn't list the casting number.

(did they (GM) even make not-square port aluminum BBC heads?)

I assume they're GM as they have the snowflake...

But mine have a leading 0 casting number: 0313436 which is on a pronounced pad and each head has no less than five Winters snowflakes cast into it / them, one small one inside and a larger one over each exhaust port...

They recently came off a running Tri-Power Corvette and I was told there's about 5000 miles on them - they've likely been rebuilt before as they're stamped "L" and "R" & "OK" by the date. They have press in plugs.

Are these experimental pieces?

Thanks again everyone!
Anthony