It looks like a steel tub, and I see what you are saying about the liner. If it is a liner, who knows what they put in there to fill any voids between the two.
Drill a hole in it and see if you get some clues, or throw an old blanket over it and give it a couple good swings with a ten pound hammer and see what breaks.
That is not a steel tub it's cast iron. It could weight as much as 180#.
Then a ten pound hammer will prove that.
There is an angle brace under the corner that I have not seen in a cast iron tub.
What he has below is a cast iron trap. And that is a piece of lead pipe attached to the bushing.
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