[Arran]

Paul;
Do all of these sets have that "wool" on the one side? If so maybe it was to deaden vibration, during the 1930s they seemed to be fixated on sound from the speaker affecting the front ends, they shock mounted everything on rubbers, the tuning cap, and often the whole chassis. On several of my sets I just let the chassis sit on the bottom since I had no chassis washers, other then the height of the control shafts it didn't seem to affect anything, by the 1940s they often didn't even bother with them mounted the chassis down on a sheet of asbestos, without a bottom cover, presumably to save on steel.
In my RCA A-20 sets they mounted the 6SA7 socket on rubbers, though they didn't bother with a sheet of thick fibrous material near the tuning drum, not that there would be much room for it. They did have chassis washers under them, and a sheet of asbestos as well, these were 1939-40 models I think, and were quite popular judging by how many I ended up with.
Regards
Arran