So I'm building a new setup. I have a J35A6 short block. It's brand new in the crate. I have 2 sets of heads I can use. First set is from a 04 TL 6 speed and I also have 08 TL type S heads. Is there really that much of a difference? I own the 04 heads but I have the option to get the 08 heads cheap.

 

well yes, the type-s heads flow better.
unless you want to port and polish the 04 heads...

 

J35A8 heads will give you 11.0 compression ratio, J32A3 heads on the same block - about 11.8 CR.