Pull one and put it on a spring tester and test the seat pressure that will tell you what it is without a doubt

 

That's a great idea for someone with a tester.
Unfortunately, I don't.

 

Im sure ANY old hot rodder around you has one.

 

Thought I'd resurrect this thread for myself & future L33 owners.

I picked up a 2005 L33 from a wrecked Silverado, and am looking into the heads/springs/cam issue.

No definitive answer in several forums, although a good bit of speculation the heads are LS6 castings, and the springs are LS6 as well.

I went to GM Parts Direct and did some part number shopping for an '05 Silverado and an '04 Z06 Vette. Here is what I found:
LM7/L59 (iron block 5.3) bare head PN 12578925
L33 bare head PN 12564825
No part numbers listed for the springs!

2004 Z06 Vette bare head PN 12564825
Z06 spring PN 12586484

There is the answer for the heads! The L33 and LS6 heads are the same PN. The springs remain a mystery, but one could conclude the use of the head would entail the use of the springs.

I'll update if I can find this out somewhere.

 

LS6 heads are larger CC chambers than 4.8/5.3 heads. How do the L33 motors get higher compression than regular 5.3's? Different pistons?

With them being LS6 heads I'd bet the springs are LS6. With under .550 lift I'm keeping my stock springs. I have some good for .620 in the garage, but thats for a future motor project.

 

those are the same springs we pulled off my stock LM7 last weekend...replaced with yellow LS6 springs

 

That is the same factory lm7 springs I took out of my 5.3 has the same green mark .I went with the comp 918 though