If you want a lazy-man's way to safely remove the liner, first set up an outdoor propane burner. I'm talking about the kind they sell to heat turkey frying pots. Set the drum up on it and fill it with water. Then dump in about half a box of Cascade or Electrasol dishwashing detergent and fire up the burner. It will heat better if you cover it. Bring it to a boil, then turn it down some and let it simmer for about 30 minutes. Then shut it down and let it cool. This solution will strip paint, grease, dirt, or oily junk off anything. I use the bottom of a once-lined drum for a cooking grate soaker, and i do the same thing - propane cooker, water, dishwashing detergent. I use a whole lot less dishwashing detergent. After just one time the liner was already falling off. Half a box will knock it out for sure.
After it cools all the way down, bail it out using a 5 gallon bucket and go dump the solution down a (funky) toilet that goes to a sewage treatment plant. Don't dump it outside or into a storm drain. We put dishwashing detergent down our drains every single day, and a little dissolved paint will be filtered right out by the treatment plant. Rinse your drum real well and wipe it out with dry rags. It probably won't need any wire brushing, but if there are any stuck-on spots, they will come off way easier after this soaking.
You'll burn a few $$$ in propane, but you will save yourself a real dirty job and this is probably more environmentally appropriate too.