At the current time I don't have the exact date (it was in 1976) for this incident but it was a Norton aircraft/crew. John Neilson confirmed the aircraft tail number was 65-9402.

This photo was taken while 65-9402 was sitting on the ramp at the
COMOX airport awaiting repairs following the 'supersonic' incident'. Due to the
resolution of the photo you can't make out the tail number, but trust me, it's
9042.
Copyright ©: Bill Weeper
Bill adds these comments regarding the supersonic incident:
I was on a C-141 crew that took a replacement set of petal doors to Comox RCAFB
Canada after the incident with 65-9402. We took the old set back to Norton. One
of the petal doors had a large chunk taken out of the door (at narrow end). It
sat there for quite a while getting repaired. A loadmaster friend of mine
(George Spaulding) was on board 402 when the incident occurred. I can't
remember any of the other crew member's names.
Bill Weeper

Copyright ©: Paul Minert, Date: November 1980

Copyright © 1976, John Neilson, Date: 2000 at the boneyard
While cruising at FL390, and without warning the aircraft nose swung sharply
to the right. The pilot disconnected the autopilot, and yaw damper. The Dutch
Roll became worse. He started a descent and regained control at FL310. After
the aircraft landed, the #2 and #3 yaw damper rate gyros were replaced and the
write-up was signed off.
The next day while returning to home base, cruising at FL410, the crew felt a
couple small jolts. They disconnected the autopilot and waited. After a few
moments when nothing more was felt, they reconnected the autopilot. Moments
later the nose slammed violently to the right. The pilot again disconnected the
autopilot and yaw damper. He attempted to control the Dutch Roll with aileron.
Within seconds the aircraft was partially inverted. The rolling and yawing
continued as pitch reached 90 degrees nose down. Loose objects flew around the
cockpit. The crew bunk mattress and the Navigator wound up lying across the
instrument panel, hindering vision and control movements.
The pilot regained control and recovered from the high-speed dive at 17,000
feet. The crew performed a controllability check and recovered the aircraft to
the nearest military base, Comox RCAFB in Canada. Large pieces of the upper
wing skin, and pieces of both petal doors were missing.
Flight recorder data indicated "G" loadings of+3.18 to -3.52 and a maximum of
450 KIAS Investigators were unable to confirm the maximum Mach, but suspect
that it had exceeded Mach 1.0.
Accident investigators found that the aircraft had experienced seven yaw
related flight control malfunctions, none given a red "X". A dual malfunction
of the autopilot junction box and the yaw damper control panel caused
intermittent spurious signals to the yaw damper, yet gave a satisfactory test
indication.