Kickdown linkage
Here's some photos of the differences between the 2bbl '66 version, the '65 4bbl, and the '66 4bbl.
Top photo has the '65 4bbl on top and the '66 4bbl below it. The middle photo is the '65 4bbl up top and a '66 2bbl below. The bottom photo is the '66 2bbl on the left and the '65 4bbl on the right. Not only are the upper arms different in shape and offset, the lower arms are different in length too.