"After the tragic death of its drivers during a recce for the 1964 Monte Carlo rally, Vauxhall withdrew from motorsport, just when it was the new perfect marketing tool "
It might be worth contacting Michael Kempley at The Telegraph, who is/was a bastion of knowledge about old rally info and seems to have been in your car for the race. He was still rallying himself about 5 years ago so if he's still around i'm sure he'd be at least interested and possibly have more of a clue what happened to your car.