Replacing the rear vent window rubber was a mean job. I did have to remove the glass in the doors, and then the whole vent window mechanism came right out. Getting the old (57 years) rubber out was not easy, and had to be chipped out with a sharpened screw driver. I carefully removed the glass from the divider bar, taking careful note of where all the washers go. Then everything got cleaned and painted. The new rubber went in pretty easy, and I must say that it has a good fit. Everything went back on the divider bar and then installed in the door. Fortunately the new rubber is soft and plyable, which made it easy to work with.
I never did get the 'Factory Fit' that I was looking for. Specifically, there is a very slight air gap at the bottom of the glass frame where it meets the rubber. Since I was careful to put everything back exactly as it came out I can only figure that the reproduction rubber is just a little thinner in that area. It is not a big problem, and certainly one that I can live with. The overall appearance is excellent.
Thanks for the advice and instructions I received.
Jack