I have the '68 doors on my current '73, went on just like the originals, and the removable window frames are the reason I got 'em.
On a '75 I had 20 years ago I came across some window frames from a 66-68 EB (like what you can now buy) and made those work with the '75 doors. The original owner had chopped & butchered the frames on mine in a bad attempt to make them removable; result was sloppy, floppy, and ugly. As I recall, removing the '75 frames was simple drilling of spot welds and a some cutting/grinding of welds where the frames met the doors. We did weld some 1/8" bar stock on the doors to make the bolt locations for the frames stiffer but that may not have been totally necessary. Worked as hoped.