Chris,
There is a slight difference between 1928 and 1929 windshield frames. If you are purest, you will probably want to buy the right style, if not you can use either a 28 or 29 frame. Note: 28/29 frames are not interchangeable. A 30/31 swing arm bracket on a frame will not work correctly on a 28/29. The 1928 frames that used electric wipers that had an offset wiper blade shaft. One of the large wiper holes was to the side and not centered. 1929 frames has the large wiper blade holes in the center of the three larger holes equally spaced. The bottom part of the windshield frames are the same for both 1928 and 1929 windshield frames. I have some pictures of the different styles if you would like to see the, Just PM me for the information. I have a 28 special coupe and when I was looking for a windshield frame (not rusted out on the bottom like mine was) I discovered the differences. Marco made up a nice picture of the frames I saved on my computer.
Rusty Nelson
Lakeville, MN