What about a cat that's clogging up? I've seen them clog up to the point where they would get hot and shoot a section of "honeycomb" out the tail pipe.
AC Delco plugs, second choice is NGKs
MSD has gone down in quality over the years. Fire Core are the best wires out right now, but big $$$ find a set you can afford in the color you want I would do at least 7.5mm. Check Summit brand first.
Are you looking to make power? Throw away the stock heads, buy used Vortecs with a China knock off intake, add carb and cam, then you'll be 350 hp depending on parts. If you go with that plan you have, about 230 on a good day.