I had a similar problem with the 440 in my Dart. It would also vapor lock from time to time. I believe your on the right track with the heat shield. That's what cured mine. What temp does the motor run?
Well the fans kick on at 180 with a 180 thermostat. Using the factory gauge set so right inside the main section by the C....I know thats not a number but thats What I have to work with.
