Installing Billet Grills
 

How difficult is it to install upper and lower billet grills on the Lightning? Is there cutting involved?

Depends on who manufactered the kit I guess. I have both upper and lower Stull grills installed on my ride, fairly straight forward with no cutting. I'm sure you could call or e-mail the manufacturer and they'd probably be willing to send you instructions if you dont have any.

Do the Stull grills replace the stock grills or do you add them onto the stock ones?

They replace them altogether.