WHere's the vent line for that tub connection? I think to answer your question, we'd need to see more of what's underneath the floor and back in the wall. Is the rest of the plumbing abs, cast iron, or continues in brass or copper?
The tub waste and overflow gets thrown out, you will need to move the drain and p-trap.
It would be nice if you can go far enough back to upsize to 2"
Some banded shielded couplings can transition to new pipe.
Given the pictures you show there, you DON'T. You need to open up the floor until you locate a 2" drain line, then route it to the new shower's drain location.