1968-74 Slant 6 head.

I run eddy 500 Avs 89 jets up Front and .86 in the rear with a Offy intake carb is pointed at the passenger fender, i get constant 20mpg with 3.55 in a 7.25 city and bit of highway nothing really over 65mph, Dart is pretty quick, since your doing the head add 340 springs and mill that bad boy to boost comp, add the bigger hyper pak valves little port job and you got a little beast! also trim guides if going with a cam over .460 lift