Old Dart 66, When I did my undercoating removal I took a propane torch and heated up the undercoating then scraped with a putty knife. Its not that bad of a job just slow and dirty. I dont burn the undercoating I just move the flame back and forth until it gets soft. I do a section of about 18"x 18" at a time. You have to be careful when doing the fender wells cause you don't want to make the metal to hot that it would distort the body. So take your time and move the torch around!
Best of luck its a dirty job and you probably save about 50 total lbs if I remember.
Rod