I've flown every variant of the 707, except the RR Conway powered -300, and the QF 707-138 (not a -120, as many seem to think) and every one featured Mach trim.
And I've flown those...so I think we've covered the waterfront with discusion re: mach trimmer on the 707...they all have one.
The -138B by the way was a tail-wagging son of a gun on final in gusty winds, with the yaw damper OFF, as it had to be.
The -320 straight-pipe aircraft was the same.
The young button-pushing First Officers of today would have eyes as big as dinner plates if they had one of these old airplanes strapped on...would be interesting to watch, no doubt about it.
