I don't know how concerned you are with authenticity, but since none of the sound-deadening material is going to show anyway, I just decided to go with a modern product. There are many choices, and it's very easy to use. Just cut it to fit, peel off the backing, stick it down, and use a roller to get a solid bond. A lot of people have had success with this Dynamat product:
I found this alternative on Amazon that is less expensive, but has worked very well for me.