Yes. that is important. the belt is different size pending with or with out A/C.

I have the GatorBack, and it's a nice improvement on those firmed up shifts!

 

I had belt squeel when i added my tuner and the gator back did the job ...
but........
it took 2 trips to checkers to get the right one.. the one listed for my '04 5.4l was literally 1 inch to short, no matter how much i torqued on the tensioner... so I went back in and requested one that was an inch longer and the right one so happened to be a lightning belt?? dunno if thats the case now but last year that was my situation??
and just to keep everything on topic....
the belt diagram is quite literally under your nose when you pop your hood! and very self explanitory! but you do need some narrow long arms and hands for the 5.4l IMO