Header flange to round pipe interface

I built a header for a /6 using an old set of headers off a v8 using the tubes and various bends as needed. I used a piece of thick wall 1 1/4 square tube as a die to hammer the tube into a square shape for the flange end, I suppose you could use a piece of hardwood to hammer into the tube to shape the end. Cutting and fitting all the tubes took a lot longer then forming the square ends of the tubes. The v8 headers provided more than enough tubing to build a shorty style header.