I was on an Aga range cooker tour of the north of England yesterday and Tuesday! I did a mini-refurb and re-insulate of a 1980's Aga range cooker in Lancashire and the next morning headed for Northumberland. I found myself driving along Hadrian's wall at dawn and had to stop, magical. When I arrived I re-enamelled the cooker and massively improved the insulation - the photos show quite a nice series.
This shows the original insulation from when the Aga range cooker was installed in the 1960's, very poor!
When I removed the top blanket you can see where there would have been big air gaps underneath, very bad for efficiency.
I topped up the vermiculite and put a new, huge!, top blanket on. All of this is squeezed under the new hob that you see below.