Right now, in KFOCI judging, only bias ply tires are acceptable for judging. Tire sizes allowed are:
47-55 Kaiser (excluding Darrin, HJ and Allstate) - 6.70x15 or 7.10x15. Whitewall width can be anywhere from 2 1/2" to 3 1/2". I have the spare from a low mileage 54K that was never used and it's size is 2 3/4".
Tire sizes like H78x15 are not permitted for KFOCI judging, regardless of their appearance (whitewall width).
Also, as stated above Goodyear was the OE supplier to KF. Judges, however, will accept Firestone, US Royal or BF Goodrich tires, provided they meet size and whitewall width requirements.
And, blackwall tires are acceptable on any car.
One more, it's been said that the real early 47 cars used 16" rims. I have one but am not sure if it's KF or Mopar since both used the same wheel supplier. If it's a 16" wheel, then the right size is 6.50x16.
Hope this helps!