Yes, they work on the HD650s. Here is what one customer sent me after ordering this replacement:
"I'm happy to report that the headband does seem to fit the HD650s - the rest of the original parts fit well and I'm able to adjust the headband smoothly. The little detents on the inside of the headband are shallow compared to the Sennheiser headband, but I think that may be due to the tolerance of the process vs the (likely) injection-molded originals. With that said, the fit is tight enough that the cups aren't sliding around, so it's probably a non-issue."
Take a look at the following video that shows the 600s and 650s side by side.