as far as the rc and cc goes its easy just cut them out and weld in some pipe. may hurt you if you have to pass emissions. My truck pulled no codes. Have not really noticed any mpg gain but i did gain some serious throttle response and it sounds great! If you are going to do and exhaust go ahead and pull your manifolds and replace those gaskets as well. And i back up the summit brand mufflers they sound really nice and they are super easy on the wallet.

 

Muffler Replacement and Exhaust Repair - Land Rover Forums - Land Rover Enthusiast Forum

Discoweb has a good DIY on cat replace that can be applied to a delete.