Try contacting Coker Tire here in Chattanooga. That whole tire and wheel package probably came from them. They have all the old molds for tires and some of their wheels are made in house.
Period correct would be 16", hard to say what's on this car...looks right to me so I'm assuming 16's. 16x4" were standard on cars and the trucks had 5" on the width.
Let's see what you're thinking about putting them on....