Started removing the undercoating today.
Used Air Hammer - worked great and removed huge chunks, but needed to clean up remaining paint to get to steel.

Tried a wire paint removing wheel. It worked slowly, but well. Unfortunately, the one I had was very old and the tines broke off. So I went to tthe local Ace hardware store to buy another, but they didn't have any.

I bought a Gator, paint remover, and WOW. It stripped half the wheel well in about 10 minutes. I would suggest using this tool, with the exception that it was $10 buck and was gone in 15 minutes. So if you have a deep wallet, buy this. If not the wire paint stripper worked pretty well.
I got 2.5 hours in... looks like stripping the whole car will take 2.5years! LOL Get R Done
I've attached a few pics for you.

 

Years ago I helped scrub clean a 1970 hemi cuda. We used propane torch with a flame spreader and 1" putty knife to get most of it off.
Wear a respirator. Try not to let hot dripping undercoating hit you in the chest!
After that I'm a big fan of 3M roloc discs.