when i did this years and years ago (ive lost all them pics in a pc crash) you buy a battery tray that fits up in the pass side at the fire wall, ( you need to remove the brace in that corner too. it never goes back on) get one longer battery stud for the original battery for the pos post, run a new bat cable from pos to pos. i ran mine across the top of the rad and zip tied it to the harness there already, then run a short neg cable to the engine block.
man i paid like 70 bucks for this damn thing back in 04 at the dealership lol
from the looks of this listing, you may need to buy the wedge and bolt that holds the battery in tight.
For 1999-2006 Silverado 1500. For 2001-2006 Silverado 1500 HD/2500 HD/3500. For 1999-2006 Sierra 1500. For 2001-2006 Sierra 1500 HD/2500 HD/3500. 1 x Passenger side battery tray,as pics shown. For 2007 Silverado 1500/1500 HD/2500 HD/3500 Classic Models Only.
www.ebay.com