as the others have said, it's supposed to be the placement of the X that makes the difference. I'm not sure there is much of a difference performance wise if you have LT's. I do and just had 40 series welded into my edelbrock catback, now I love my car all over again
For the shorty header or stock manifold version it comes in 5 pieces 2 tubes that connect to the manifolds the X and 2 tubes that connect to your catback....they have to be welded together...it does bolt to your manifolds and your catback just where the 4 tubes connect to the X is where it needs to be welded.
The LT version is 7 pieces and is basically the same thing just a extra 2 pieces that have to be cut to match the length of your LT's.
I did the welding myself in my garage it was a PITA but with access to a lift it should be a easy job to do yourself otherwise just have a exhaust shop install it for you
its not that i am too lazy, but i do not know how to weld. and plus if i brought that to an exhaust shop for a price quote, i know they would try to rape me like an Olsen twin for a job like that
Ah!!! maybe not.... from the website "These shortie/stock manifold systems do not fit under automatic transmissions." So this means I cant get one?!?!?