Boy, that looks familiar! I feel your pain, brother!
For the thinner stuff, I found a sturdy putty knife and hammer worked best to separate the foam from the metal. For the thicker, I used a pry bar with a wide blade to break off most of it. There is no solvent known to man that will dissolve that stuff. Believe me, I tried them all.
And that is one reason my warmer project is sitting in storage at the other house still.
Any tips on how you separated the interior from the foam & shell would be welcomed. Without tearing into mine, I still have not wrapped my head around how they put it together (at least where I can take it apart without destroying it). I "think" if I pull the flat jamb panels which are riveted in on the inside edge of the door opening I may have access to the interior shell like I see in your photo. Looks like it pulls out and then the top piece. But I'm not certain. And if you happened to take some photos of that portion of your disassembly, can you post them also?