There are three kits. Your engine will be either Conti CT884K1 or CT990K1. The difference is the backplate for the tensioner and upper idler roller. Both these kits contain a lower idler roller with eccentric adjustment. The third type CT990K2 kits have a fixed lower roller, ie without eccentric adjustment. These are mostly original fit on 2.6 & 3.2
The belts are all the same. Regardless of brand, if the backplate in the new kit is not the same as the one on the car then swap over the new tensioner and idler onto the old backplate.
ContiTech CT884K1 for engine numbers <=08300418
ContiTech CT990K1 for engine numbers 08300419 <=> 08578511
ContiTech CT990K2 for engine numbers >= 08578512
Conti CT884K1 = Gates K015453XS
Conti CT990K1 = Gates K025453XS
Conti CT990K2 = Gates K035453XS
A ContiTech kit is as close as you can get to a factory fit and there is no difference in the installation method.