It wasn't rockwool, Lee, but if that's what you want to call it, please go right ahead. What GM used was a jute-like material that was a mixture of felt, paper, linseed oil, tar and tow fiber. It was compressed into about 1/4" thick rolls, cut with large steel rule dies and stuck to body panels using a sticky brown glue that reminded me of the stuff you'd use to seal flat tar roofs. Until about 1980 I had a gallon bucket of that stuff that was about half full and I used it to bond carpet in an MG I restored. Neoprene was invented in the early 1930s. Not too many spacemen flying around in those days.
I think I may have installed over a dozen of these, and yes I do know there's not a great deal of space in places. A few years ago I told folks I would use Formica instead of the cardboard because it won't buckle, warp or deteriorate.
