It will. as stated, be number 53 in the Disney Classics range.
I'd assume it'll use the newer designed number on the J-card as that is now the Disney standard. However, the last few steelbooks still used the yellow oval version even though the new style was on other releases by then, and even on the discs inside the steelbooks.
Planes is not a Disney classic so has no number. It was part of Zavvi's Disney steelbook collection, but that in itself really means nothing. That's just a list of steelbooks exclusive to Zavvi (in the UK) and contains frankly whatever they feel like including, ie: it did contain Planes and Mary Poppins, but not Maleficent.
It depends really on whether you collect Disney classics steelbooks, Disney steelbooks in general or Zavvi exclusives (or all of the above). I collect all the classics, all the Pixar titles (which includes HMV's Cars 2) and others that take my fancy (ie: Tron, Maleficent and Mary Poppins but not Planes).