Do I been an AUX idler for a 2.90 metco?

[2001asp]

Hey guys I have a 2.90 Metco pulley nib. I plan on installing this very soon. Will I need an AUX Idler, or will I be ok without it? I also have a 100mm idler pulley that I can install. So do I need a new belt? Or will the stocker be ok? Car has jlt ria, pypes x-pipe w/ metallic cats, Borla stinger, and currently tuned. Car makes 421hp currently and hoping to break the 475 hp mark after pulley install and retune. Thanks for your time.

 

[SJ SNAKE]

Yeah you're going to need:

1.) Auxiliary Idler (100mm is fine and will lower belt slip better than a 90mm would)
2.) New Belt ('Gates' or 'Gatorback' in the size of 75.50 inches I believe)