That one looks like it's been modified, but there was a factory split exhaust manifold for the 6 cylinder Corvette, and thousands of them were sold by Chevy parts departments and used on 235 and 261 engines. If you've got a bit of experience welding cast iron, any exhaust manifold can be split, but it's a little more complex than just adding a second pipe flange. A baffle must be inserted to almost, but not quite block off the flow between the two pipes. That approach, even if a stock manifold is modified and the OEM manifold is not used, is far better than the "Fenton" knockoffs that eliminate the heat riser.
Jerry
