May help.
The company was BOAC, I thought the incident was out of Dorval, Montreal (but could be Toronto), probably a -436.
The conversion course we did together was in 1978 and I had the impression the incident was some years previous.
The chap was a captain on the 707 by then, so, if in the incident he was a P2, it possibly happened in the 60s.
I joined BOAC in 1970 and don't recall it happening in my time, but that may be because I was on the VC10.
I know that D P Davies, of AAIB fame, was closely involved in the investigation (my acquaintance was not very enamoured with him).
He stated that the trim even ran away with the brake on (wasthere a brake?) and his hand trying to stop it.
Never flew the 707 but I think it may have been something to do with the servo tab working in the wrong direction.
I know the name of the person involved (we shared a house in New Zealand on the ANZ DC10 conversion course) but I will not reveal it here.