Are you sure about that "no Mach trim" statement? The NTSb report on the Egyptair B767 specifically mentions Mach trim in its discussion of the pitch axis controls....
Not according to my Boeing Tech refresher..perhaps the system is incorporated in conjunction with another system, rather than stand alone as per the 757.
There are certainly no QRH or failure items for it in the FCTM (flight crew training manual)
A non Boeing Link
767 Autoflight Systems Information
The 767 autoflight systems include the autopilot/flight director, yaw damper,
automatic stabilizer trim, Mach trim, maintenance monitoring, instrument landing system
deviation monitor, and thrust management systems. The thrust management system
includes autothrottle control.
Straight out of the NTSB report...although there is no Mach Trim light on the 767 overhead.