If you look at the MSDS, Ilford seems to use DTPA instead of DAPTA in their product. Which is good because DTPA is much easier to get and cheaper ...
There is no guarantee that this formula is anything like DD-X. Patents often contain such formulas as proof of a particular concept. Companies may try various methods of obfuscation and may even leave out important ingredients.
My understanding is DDX is buffered (Borax-Boric acid).
EDIT 1: Rudeofus prefers DTPA. Interestingly, the patent says "The preferred sequestering agent is [...] DTPA." So why didn't they use it in their sample formula?
EDIT 2: Looking into this some more, I see that the MSDS for DD-X specifies (1) Boric acid (Michael R mentioned this), (2) Dimezone S instead of Phenidone, and (3) DTPA instead of DAPTA. So I'd say the patent was for an early formula which the engineers improved later. Based on quantity-ranges in the MSDS, I'd say this is similar to DD-X. Given this patent-formula and the MSDS, it wouldn't be hard to reverse engineer the present formula. Anyone want to try it?
Sequestering agent isn't so important part of formula from patent. More interesting that developer omit any antifoggant (KBr, BZT etc)
working solution 1+4 must be like to next:
Potassium Sulphite 71g
71g of Potassium Sulphite = 71/MW(K2SO3) = 71/156.26 = 0.4544M = 0.4544*MW(Na2SO3) = 0.4544*126.04 = 57.3g of Sodium Sulphite
Older MSDS data for these developers is very much more informative, they show that Phenidone was used originally in DDX.
DTPA is no exception (see page 6). Choosing a different sequestering agent can give you a different pH and buffer strength! Also note that the patent lists DTPA, while the MSDS lists DTPA pentasodium salt, the first one is a strong acid while the latter one is caustic (and much easier to dissolve). If pH is suitably chosen there is a good chance that no restrainer is needed.