Exhaust Damper/Heat valve
Cut it out, weld up the holes and never look back. Use the Felpro gaskets that block the crossover in the intake.
If you are big on everything looking stock, weld up the holes on the inside, cut the pieces off your old heat riser and weld or glue them in the holes, but when was the last time you looked at a manifold to check of the heat riser was there?