That filter element is way too small (short) to give a 235 enough air at speeds above a fast idle. Yes, it will run rich because of manifold vacuum finding its way up to the venturi. It's like running the engine with the choke partially closed. Try stacking two of those elements together with a thin wrap of electrical tape or black duct tape to prevent leakage where they meet, or just find a taller element with the same diameter. Another method would be to use a thin bead of RTV sealer between the two filter elements when you install them. We used to do the same thing on the dirt track race engines, to make a filter element nearly a foot tall. A small block V8 at 7000+ RPM needs a lot of air.
Jerry
