anybody know the difference without measuring dont have heads in hand, between the two heads (both have same casting #'s and gm part #'s)

 

The only difference between the two is the LS6 heads have sodium filled valves and the LS2 dont. I am not sure but the only way to check is to take out the valves. Its not a big deal ether way, they both flow the same and have the same CC. Hope this helps.