I used these in my build . They are made in china cheapies but only 200 bucks including shipping and no trimming or cutting of frame nonsense.
http://www.ebay.com/itm/C-10-GMC-C10...27866d&vxp=mtr
If link doesnt work just go to ebay and type in c10 ls swap headers and the first few listings is what your looking for like 185 no shipping or 200 shipped. They slide right in i have a 6.2/6l80e and they fit your 5.3 no problem im guessing .. GOOD LUCK
