I've been running the old hipo manifolds on a variety of small blocks in a variety of 1967-76 A-bodies for decades and have never used a factory heat shield on any of them. I gave up on headers on my street cars for the same reason - poor performance after damage.
another tip: if you care about looks, use the POR brush on exhaust paint. If a bit peels or gets damaged from oil or brake fluid, you just touch it up with a small brush, start the engine to melt the paint and the brush strokes disappear and it all looks fresh again, without any masking or manifold removal!
