64 kick panels are the same as 65-66 except that they don't have the top "windlace" cover part at the top. The 65 and 66 panels are the same. 67 has the vent pulls incorperated into the kick panel.
All will fit, but only the above is correct.
I believe only the passenger side A/C kick panel is unique, the drivers side is the same for all. The AC kick panel has a squared off top to provide room for a vent? I have never owned an A/C car, so I don't know what the room was needed for.
If you are looking for 66 kick panels, remember to look for GTO, cutlass and Skylark panels too. 2dr, 4dr, El Camino, wagon and convert panels are all the same.
Do a search for refinishing kick panels, there are special products for repainting them with successful results.