To answer your original question....yes. I've gasket matched my 273/4 engine and cleaned up slag and other casting flaws so that the gases flow a bit freer. I slicked up any rough casting where I could reach with a long shanked grinding stone. Beyond that, I would have to extrude hone them for the ultimate in flow. I couldn't justify that cost for street use. I also did other engine mods, so, trying to compare a performance increase for just the exhaust changes would be too hard to determine.
