You won't find a small diameter stock wheel from that era. All the cars had large wheels, as power steering was an option on most vehicles then, and you needed the leverage to be able to turn the wheel. Nardi is one of the brands that make wheels that will fit with no problem. There are a couple of other brands as well. Some have real wood rims that look very classic, too. Failing that, you may want to get the wheel out of a later model Ford. It won't look original, but it will gave the smaller diameter you need and it should fit with no problems. By later model, I mean the late-70s Thunderbirds. You might even get lucky and find one with the correct colour, depending on the colour of your interior in the 56. Just be sure to keep and preserve the original wheel so it can be put back should you decide to sell the car.