Are all door handles the same 64-76?

The 68 s did have black buttons. There was a slight change in the mechanical design behind the button too. If you buy reproduction handles you'll need to reuse your original mechanical parts. If the button sticks when pushed now you'll need to clean, lubricate whatever to correct that. Repeatedly hitting down on the top of the handle to get the button to pop back out will either break the handle or more often crack the door skin. I suggest you have the originals re chromed. The repops and some that are supposedly NOS that I have seen dont look as good as some 40 year old pieces.