340 has no balls

Well ,been driving my numbers matching 69 340 dart around . Car doesnt have any balls to it . When i get on it , I seem to hear the pistons rattling .Ill try some better 110 leaded gas when I can and check timing but to me . I think Im looking toward a 455hp /408 crate engine . That should get things running the way i like .I dont want a slug on my hands.