Early '30
I just rebuilt an early '30 generator. Looks just like this one, with post at front, no holes in the end plate and wick oiler.
In looking at the side view of your generator, my attention was drawn to the band. It looks like there might be some numbers and/or letters on the band. I am looking at the center of the band in the center of the picture. If they are there, they can tell you the month and year of manufacture. Of course, the band could have been switch over the years.
'12J' is December 1929. If you find it - post it. Someone will know; That's how I learned about my number. Bill