Can anyone give me an idea on the vintage / model of this disk?

Its an 8' John Deere, but other than that I didn't really see any identifying marks. It's pretty old - with plain bearings and no transport wheels. The angle of the front set can be adjusted by pulling a lever and sliding the arms up the tongue.

I picked it up this weekend and used it to turn under about 4 acres of sage infested alfalfa. My 83 JD 750 pulled it great.