If dead nuts originality isn't an issue, why not just drill four small holes in the support, and fit it with a more common radiator? Nobody will ever know the difference.
They may have had to move things around on the core support to be able to get that width. As often as these one year 1964 273 radiators are asked for I would think someone would have posted details on how to use a 22" core radiator on them if it was feasible.
If you aren't worried about staying original why not go aluminum that offers better cooling than the OEM radiator? Personally I am a purist but when it comes to drilling holes in my car to make something fit or buying aftermarket that will fit in the opening, I would go aftermarket and continue the hunt for the OEM radiator for my car.