I might be able to get a set of heads from a 5.3L 2012 Colorado, I think they are 243 castings same as LS6, but does not have the sodium filled light weight valves. Will I loose a bit of compression going to those heads on my 2007 LR4 4.8L (from a Express van)? They will definitely flow better. As far as I know the late 2008 to 2012 4.8L and 5.3L come with the 243 heads, and use the same pistons and rods as the earlier year motors do, the newer ones make more power..is that were the gains are?

I'm thinking of swapping in a LS6 cam as well, will I need the yellow valve springs as well? And LS6 push rods? I can use my stock lifters though right?

I might pick up a set of LS2 injectors as well! My goal is 330-340 HP at the fly-wheel, and about 325 ft/lbs. I'm currently about 300+ HP and under 300 ft/lbs at the fly-wheel