As others have said, a 216/235/261 exhaust can only be split 3 & 3. Years ago we used to cut the stock manifold right behind the center outlet, then weld a piece of cast iron across the hole. Then we used a Fenton cast y-shaped rear manifold, similar to what Langdon sells now for the later engines. The flanges were the same and used the same doughnut gasket. They flowed well and sounded good too.
A tube header is more efficient if it is done properly. The 2-3 and 4-5 tubes need to be larger diameter than the 1 & 6 tubes. I haven't tried stepping them, but that would probably help. They don't sound any better and they are more prone to leak, but they help the power if the primary tubes are the right length.
