Exhaust for 2000 GT
 

I'm thinking of adding a Bassani X Pipe and MAC catback exhaust system to my stock 2000 GT.
First does anyone know if I will I have any problems installing these two pieces together?

Second the May 2000 issue of 5.0 Mustang magazine ran a dyno test on an X Pipe install on a 1999 Cobra. They mentioned that the Air/Fuel ratio should be changed when the X Pipe is added. The magazine claimed that it was worth almost 14 Hp extra just by changing the A/F ratio. My question is should I change the Air/Fuel Ratio? If so how do I do it?
Thanks for the help.