Just get the ones that fit your application year, in that case it doesnt matter too much, you are going to need to get a Midpipe anyways. I am pretty sure that MAC makes their LT collector size 2.5" so I think your safe there
This header guild mainly applies to those who have a 99-04 model and are looking for extra performance cheaper than they can with aftermarket headers. It also shows the 94-98 guys that their headers are great as they are and really dont need to purchase a $400 dollar set of shorties