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The casting is the same, however the 02-04 heads have light weight hollow stem intake valves & hollow stem sodium filled ext valves.
I think there may be spring differences, also. I believe the 2001 springs were one color, the 2002's another and the 2003 & 2004 springs, no color. I don't know the significance of that, only that different color (paint) springs were used. Hopefully, someone can chime in. Maybe the springs were the same but the spring supplier was changed...don't really know.
Ed
Heads are the same 01-04, 01 has the lightened valves ,blue valve springs and a smaller cam.
The valves were lightened in 2002. 2001 intake valve weight was 99 grams, 2002 was 76 grames. 2001 exhaust valve weight was 86 grams, 2002 was 63 grams. Take a look at this link for a detailed description of the differences between the 2001 and 2002 LS6 cams and valvetrain. http://www.idavette.net/hib/02ls6/page2.htm
Ed
