There are split exhaust manifolds for the 235s on ebay almost all of the time. As Longbox55 says, some are "rather sloppy."
Back in 1955, I bought a split manifold kit from Almquist for the 235 in my '53. The kit consisted of a short manifold for the aft three cylinders with an exhaust pipe flange, and hardware and instructions for modifying the original manifold to accept the new aft manifold. What I had to do was to cut-off the aft portion of the original manifold just aft of the heat riser and stock exhaust pipe flange, using a hand hacksaw. Instead of welding a plate over the hole now in the stock manifold, Almquist provided a plate, gasket, and jack-bolt that sealed the hole without welding. Has anyone else seen this type of split manifold? The one that i had is the only one that I have ever seen.
This system worked perfectly. However, I replaced it in 1957 when I heard about the Corvette six dual exhaust manifold. The Almquist split manifold kit cost about $30, and the new Corvette six manifold from the local Chevy dealer cost about $13. I would not be surprised if the Corvette six manifold might go for a little more than that now.
