Bobby,
I believe 51 was the first year of the vent windows. So, anything prior to that would have had the one piece windows.
If I'm not right, I'm sure someone will jump in here real quickly and correct me.
As for the glass, once you've either changed or modified your doors to accept the full window, I think you'd probably be better off to just have new glass cut, rather than trying to fool around and find half decent used glass.
Most any auto glass company, or regular glass company for that matter, should be able to cut you a couple of windows fairly inexpensively.
