Intake 'manifolds' are basically the same for the LS1 but the cold air 'intake' is different (trying to help clarify what the originator of the thread was trying to ask, I believe). Interestingly, pre 2002, the intake 'manifold' on the LS1 (aluminum block and heads) was different than the one on the 2004 GTO. The 2004 GTO has the LS6 manifold as have 2002 and later LS1s as I recall (I had a 2000 C5 with the LS1 and had considered putting the LS6/2002 and later LS1 manifold on it for the extra 5+/- it was claimed to yield). K&N and Lingenfelter both make CAIs for the 2004 GTO with TB to MAF connecting pipe that fits the GTO. AEM is reportedly coming out with one shortly as is, I believe, at least one other (either Vararam or Volant----can't recall).