If you got that info out of an aftermarket (non GM) parts catalog, I'd be careful trusting some of the info. I see mistakes in a lot of mine at work concerning the LS motors, and I can't tell you how many times I've seen the LS1 listed as a 350CID motor

 

Which ones of these are the dreaded Castech heads?

My '06 L59 5.3 has the 706 heads, FWIW.

 

I know when I was at the shop last week I did see this head there 853 aluminum it had5.7 on the inner part on one of the ports. I have a buddy that works at a GM dealership that gets me all of this numebers what goes with what.

 

and ls1's had different heads every year till 01 i think. 97/98 werid bolt pattern. 99/00 some head lol and 01 up had 241's