I have a number of WBCs that take the standard National size boxes
The WBC floors are open mesh and have been designed to accommodate the National Boxes, the sliding blocker system is far better than anything I have yet seen on a standard National floor set up, however if you want to move any WBC they are a pain!!!!
I also have some older WBC hives manufactured by Robert Lee and in these the boxes are much smaller with thin walls, the Brood Boxes will take 11 DN4 frames, but will only fit the outer covers the cold way, the supers take 10 (or 8) frames on castellated runners.
I have seen.... some time ago a National sized hive that looked like a WBC with sloping covers fixed to the supers, that then overlapped the box below, I seem to recall that these were being made by a beek in Croydon, but were very heavy.