I'm going to add something to this discussion. I have read that the "asphalt-like stuff" used as undercoating years ago contained asbestos! I cannot confirm that, but when I was working on my 1948 Plymouth, some of that stuff I encountered was difficult to remove, even when heated with a propane torch. I'm just suggesting that you realize it might
have asbestos in it, and take some precautions when removing it.