Does anyone know who this lowered rear end belongs to?
That looks like the setup that Clayton Padison came up with a few years ago.
There were brackets available for similar ways of lowering the rear back in the day: http://www.nwvs.org/Technical/TimKnappOnLowering.pdf
Don't know who's build is shown in the picture - it isn't Clayton's roadster. It gives a lot of lowering so Clayton rebuilt his later to make the lowering adjustable with long shackles and a panhard bar.
I have built a similar bracket as pictured for my 26 roadster and may get trouble with clearance to the frame and body.. It's easier to use this method on a speedster without much body to consider
No this isn't Clayton's roadster, I have followed his build pretty close. I like the simplicity of the brackets and shackle in the pictures though.