KXF sounds like a cool project, I have a 75 C15 short step with a mild 454. Id recomend either Edelbrocks Performer RPM, or Comp Cams XE274.
as far as atleast 400 HP, youll be more like 500HP no problem. as far as Carb, right now I have a 770Holley on mine now & love it.
Im eventually planning on buildin mine , I have the same heads & was shootin for same compression with LS6 pistons, when I do Ill probably use my 800 mech. sec. on it.
have fun, let me know how it turns out. John