whats the difference between the different casting numbers of the 5.3/4.8 heads?

 

I think they're all pretty much the same until you get to the later 05+ 799 castings. The 799's are interchangeable with the 243's. Larger valve, 64cc combustion chambers, improved flow.

 

alright, I was talking about the 862 heads and 706 heads, I tried reading around but just wanted to be sure.

 

If I am not mistaken the only difference is in the way they are cast. 706 uses a Semi Permanent Mold process and the 862 use a sand cast process. Its said that the SPM process is a little more precise. You can find a little more info in Will handzel's book "How to build High-Performance Chevy Ls1/Ls6 V-8s" Alot of detail and Backround on the Gen 3 Platform.