New Body and Paint

You can do what you want, but I would never paint an older car without stripping down to bare metal. I would consider allowing the current paint to serve as a base for a paint job on a newer car, because it will be painted with modern Base/Clear paint. But you have no idea what is under the paint on a 50 year old car. There could be three layers of three different types of paints, crappy rust repair, super bad body work with 1" of Bodo poorly applied. You won't know if you just paint over what is there. In my humble opinion, don't do it.