My amazing Stiffel find- what is it?

I recently acquired an unusual Stiffel light fixture. It appears to be hardwired, no switch. It is a two piece swag set and I assume it is brass. I don't believe the glass shade in the picture is original because there were three other matching ones. It has amazing detail work on the chain.
Like any Stiffel it's heavy - it does have the sticker on the bottom and the original tag. But this a beast. Hanging it will be an engineering feat. It is over 15 pounds and is 48 inches long without the shade, which adds 6 inches.
I love this lamp but I'm so curious about it's age, etc. I can't find anything like it online. Any ideas?

I'm hanging it in the family log cabin. As soon as I figure it out, I'll repost! Thanks