Are 1964, 1965, and 1966 barracuda and 2 door valiant doors the same and interchangeable?

The main thing to keep in mind is that the striker assembly is different on a 63. To make a 63 door work on 64-66 you will need the cut the striker opening larger in one area and move one of the mounting holes. It ends up being a rather ragged looking modification if you don't weld in a little filler metal and flatten and fill the original hole. It can be made to fit though.
You will also have to transfer your wing window assembly as convertible wing windows are different.