The 1965 and 1966 impalas used an idler arm with the vertical through bolt and Nut on top of the chassis. The 1967 to 1970 chassis used a different drag link and idler arm which bolted sideways through the chassis rail.
The Rear axle trailing arms are also different on 1967 onwards, with shorter upper trailing arms and different arcs of travel. the 1965 rear axle also has different trailing arm mounting holes. best to keep all parts that came with your new chassis.
Convertible frames also have an additional body mount on the chasis, and stronger side chassis rails.
