Mach tuck was very pronounced on the 'ole 707, above about .84, and would often result in the stab trim running near to the full stop, if not caught in time...that is, if it didn't bind up the stab jackscrew beforehand.
Definitely NOT a good scenario.
Correction technique, power off then split the spoilers to get the nose up, and it was right in the QRH...clearly it had offered up exciting occasions before.
