To my knowledge only 12 cars actually left the factory in 1968.. R7012 being the last for car 1968, I have one of the 12 cars.
R7662 would not be a 68 car but a 1973 car.
I think the only registered 1968 cars in the UK at the present time are chassis numbers
R7001, R7003, R7006, R7010, and R7011 anyone know of any others?