There is no question about it that TTI makes the best headers for the "A" body MOPARS no matter if it's for a small block or big block they are high quality headers and worth the extra cash.
But you really need to get that MOPAR in for some serious undercarage cleaning. I had my 72 sand blasted underneath while I had the car totally stripped down so every nock and cranny is clean as a whistle. Now I'm going to get her either epoxy primmered or a light coat of undercoating before I assemble her. It will be clean clean clean underneath. Being as the car will be on the street on rare occasions it should stay clean for some time.