That looks very interesting but I suspect that it could not be used with the 'beaks' on the standard side panels. Anyone know any better?
I've just measure mine which was bought new about 50 years ago. It is 3.5 inches deep and about 14 inches side to side but the sides are tapered so it is narrower at the top and wider at the bottom by about half an inch per side. Incidentally the brackets are plated (?zinc) not painted, but painted will look