...After doing a quick search, I've seen people say there were other drives sold as this HiVal, so it will probably be easier to open it up & check it manually as KTL suggested.
I wouldn't try to flash any firmware before getting verification.
That said, if you are willing to burn a single layer DVD at 8x or 12x, you might be able to tell from the write curve (using Nero CD-DVD Speed/DiscSpeed or OptiDriveControl).
Between the 1640 and 1650...
The 1640 will reach 8x/12x in CAV mode, then switch to the CLV portion of the burn for a little while. At a certain point, the drive will drop the RPM to avoid a resonance issue. The speed will then recover to 8x or 12x in CAV mode, and will continue in CLV mode.
The 1650/1655/etc, once they reach the CLV portion of an 8x/12x burn, will remain at 8x/12x CLV.
Other drives have different write curves, and/or can be identified by a different drive ID (I assume).