If its just factory paint then you can just sand and prime. No sense in going down to bare metal unless you have to, its a lot of work time and money. AL
Sure its a lot of work to go down to bare metal, but even without that, its a lot of work and a lot of time and muscle is tied up into bodywork and prep on a typical car that was made 1967. If it still has factory paint and primer on there, it would be unactivated enamel or a lacquer, which could cause problems if you paint over it or even if not, it will be a less desirable product that will still be setting the foundation under the better 2k products used today and could bite you a little down the road. Taking it down to metal will give you the opportunity to see what that car has had happen to it, any shoddy repairs, or what needs attention that you may not realize if you don't take the paint off and just start with that. Starting with baremetal will give you the start to a good foundation of epoxy and other 2k products, as well as being able to see exactly what condition body you are dealing with, before you start laying on products and paint which is fairly pricey today. Its a little more work and money to strip it all down and start fresh, but a smart move IMO unless you know the exact history of the car and exactly what has been done to it and what is on it. The amount of extra work/money is not worth the risks at least in my opinion. The price of body materials, media, and extra sandpaper is cheap in comparison to paint materials. You know that all has been sanded or blasted well to spray the epoxy on when its all off to metal, every spot had touched by media or sanding to get all the paint off and down to metal, and should have good tooth for the primer/ as opposed to sanding paint where you may be using a scuff pad to get in hard to sand areas. It will take up a little more of your time to do it right. Aaron is right, if paint is flaking, it needs to come off, and you never know if panels that aren't flaking at this point will in the future. If it was a realitively new daily driver with a modern finish, go ahead start over the factory finish. A car is almost 40 years old, trying to avoid accidents, winter, and all the other things thrown at it, that just may have old 1k products, and you have been sticking money into and want your best chance for a long lasting paint job -I think the smart thing to do would be starting fresh when paint and materials alone can easily pass $1000.