I believe M59 and M59/66 magazines are identical.
Here's the magazine off my Clayco M8. One of the latest manufactured mags I've got:
Compare to a follower arm from a 2 mil Sino-Banian with no twist:
I think your magazine is a later model Chinese. Very close to the M8 mag. They are very similar, not identical as the aft button for lockup wih the trigger group is totally different, but the twist in the follower arm and the spot welds are pretty close indeed.