Which part# do I need on my car if I am using ls6 style heads.

I know one says it is for 97-01 and the other is for 02-04.

But they had ls6 heads for 01 and 02-04 as well....so which ones do I need?

Does it matter, I have heard something about a water port difference?

Whats the difference?

Is one graphite and one mls?

GM part #12498543 (97-01)
or
12498544 (02-04)

thanks a lot