I have used muriatic acid to clean concrete and even Concrete swimming pools in my youth. Never used it for rust removal though. If it leaves the Iron grey and spotless I will be going full acid bath. Clean is good.
Lately I have been using electrolysis to clean up rusty parts. It's my new favorite way of dealing with rust. No damage to the base metal and no harmful chemicals, heck... I don't even use up any expensive elbow grease. If you have never witnessed a bucket of washing soda and a battery charger do it's thing... It is worth finding an old hunk of iron just to see how well it works. If not now, for projects down the road.
The nickel will get a trial run with TB cleaner. That's pretty late in the game for me. I want to get the stove body cleaned and reassembled first.
Off to the shop to start pulling her apart. I should have some pictures of the tear down up tonight.
If only I knew where my 1/2" 8pt socket went