Years ago I bought a '74 Dart Sport with a good running 383, '67 915 closed chamber heads. The car came with 456's which proved to be too much on the street. My intention was to have fun with a street/ strip car, but my trips to Englishtown amounted to only a half dozen times a season, so, ultimately I chose 391's which were a much better fit for my purposes. I felt only a minor difference in grunt. A 200 mile trip to Carlisle in July was stressful, but the car ran 12.40's consistently on street tires. It really depends on your priorities and being honest with yourself about what your plans are for the car. You will get used to the 391's. Good luck!