Barry, my Ilford trays are slightly smaller, which is why I have them. Years ago in another darkroom my sink area was quite smaller, so I went for the minimum.
My Ilford trays are 483mm by 410mm external measurements. The flat area in the Ilford trays is approximately 420mm by 350mm.
The Ilford trays don't have the Patterson external spout in one corner. Their spout is a slightly lowered corner for pouring out, compared to the Patterson spout.