LT - take those headers to the parts store and get your money back. You do not need full length anyway. I don't know where Hedman headers are made but it sounds like they are cheap made, and did not get it right! Something isn't right here as there is alot of difference in frame width and steering box position, engine heigth between the frame rails and clearences between the 55/59 and the later 60/66 trucks. Anyway there are several quality brand headers on the market, and block huggers are what you need. You will need 1 1/2" drop to a 2 1/2" or 3" collector. If you had a big inch SB you would go with 1 5/8", but think the 1 1/2" should be just right with the 283. Some quality brands are Sanderson, Thorley, Borla, Gibson, and Jardine. Don't cheap out, buy quality stuff. They can be had painted, chromed, stainless, or ceramic coated. I always buy the stainless as it will last longer than the engine and the truck and will not corrode. Go with a quality exhaust behind them and you will be set up just fine. Go to -
www.sandersonheaders.com 
