maybe you found yourself a prototype of the 35- 70 2.8!! or could be that someone had it modified with a larger focus ring for use with video cameras. i ve seen people do this to a tokina 12-24 f4. they basically change the housing and the focus gears to give better responsiveness and accuracy.
best to check with nsc. or post some pictures from the front or other side of the lens? anw, do let us know when you find out, im quite interested.