Hello, Still working on my 71 chevy c20. My 5.3 is out of a 01 truck. I have built a dual stainless steel exhaust system , 2 1/2 tube, 065 wall thickness. I ran it outside the frame. The mufflers I went with are the 22 inch Magnaflows like most of you all suggested. I am now trying to figure out " How many o2 sensors do I need? " I have no cats and are smog exempt. I am thinking 1 for each side near the stock manifolds like OEM? . I am useing the factory wire harness. On a budget. All imput is great. Thanks for reading my post. Alan