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Simple answer is "yes, but..." I have seen several posts of people who have installed windows in the doors of vintage trailers, and I seriously considered doing it myself.
A year or so back, I was completely rebuilding/reskinning the door in my '73, and I had dreams of putting a window in it as well. What appeared to be the easiest solution would be to use the same window that is installed in the doors of, say, the International model, but it turned out that it wouldn't work for two reasons. Foremost was that the window had less of a curve to it compared to my door as it was made to fit the wider body modern trailers. Second was that the price of the new window alone approached $500 if my memory serves me.
So, if your door is the same width as the International model, and the body is the same width, then you should have no problem sourcing the window, but it will be crazy expensive. Installing the window is not such a big deal, if you are not squeamish about cutting large holes in the skin of your door, and have some skills with olympic rivets.
A more expedient solution may be to look into getting an entire door (salvage?) with a window already in it. In my experieince, doors are tricky business. Every one seems to be custom fit to the frame, and they are usually tweaked so that you can't just take one from traielr to trailer and have a perfect fit without some sweat, stress, and fiddling.