The header is a WTC(wrap to center) one used on r/c boats.The tuned pipe I have never seen.A Homelite in an r/c boat uses a 0 band pipe with the center where it's welded together at between 12 1/4" tto 12 1/2" from the engines exhaust opening face.Adjustments can be made from there,after testing on the water.You find all kinds of claims and junk on Ebay.