I looked at a dart with a 440 in it, tti headers and flaming river box. ugly! one pipe was smashed almost closed to clear the box. looked like the box moves higher up in the chassis and in this case had big time header problems. cast manifolds may not be as big of a problem. anyhow, i'd do a factory box and not have the headache. aren't those flaming river boxes chevy boxes that have been "adapted" to bolt to a mopar k-member?