I've seen a few small block 2bbl Kickdown linkages on e-bay but very few 4 bbl linkages. If you're just upgrading to a 4bbl and keeping the same transmission, you just need the rod between the the carb and the pivot point. The 4bbl rods have an outward bend (when looking from the front of the car) in them since the 4bbl carb is wider than the 2bbl carbs. Year One and a few other places sell new kickdown linkages (all three pieces plus pivot, spring, clips, etc) but they are not cheap ($350 to $410).