For safety - original bench or switch to bucket?
A new car in 1967 had more safety features than a new car sold in 1960 (or any other year before 1966). However a new car in 1980 had more safety features than that new car sold in 1967.
If safety is your main priority I would consider not driving around in a 1967 car (relative to any newer car). Bumper design, crumple zones, seat belts, collapsing steering column, etc all factor into how safe a car is.
The odds of not being injured or seriously injured are a lot higher the moment you decide to drive off in an older car relative to a new car. We never plan on getting into accidents but I think it will be hard to quantify how much safer bucket seats are compared to bench seats. Having a head rests on either helps but the lack of crumpled zones, bumpers with shock absorbers, etc all play a role too. Safety advanced a lot from the late sixties to the mid 1990’s. Heck the government mandated head rests on all cars built after Jan 1, 1968.