I build my own header pipes out of (get this!) old school chairs! nice mandrel bent pipe that 1 1/4 flex pipe fits very snug. Make my own flanges, just trace the gasket on 3/16 plate and cut/grind/holesaw to near factory perfection. I use equal length pipes and make a collector out of 2 1/2 pipe 7-8 inches long. Put the big pipe in a press annd using 2 impact deep well sockets that are the same diameter as the flex press into an oval. then use anything as a wedge finish bending around both sockets. makes a sweet sounding system.
Lester