I think the flanges that Indy sells are for a 1-7/8 tube. Thats what Ryan told me over the phone. I am building 1-7/8 X 2 X 2-1/8 with a merged collector with a 2-1/2" pinch back up to 3-1/2" secondary exhaust. My Primaries will be super long since I make them to fit the car.

6400 RPM 501 Cubic Inch Indy 360-1 245CNC 48Deg Hyd Roller cam.