Good Idea checking on some plumbing advice. First off that is the old tub works you have there. You P-Trap is below the back overflow side closest to the wall. You will need to remove the fire stopping that surrounds this piping and cut out that old bath overflow and waste section. We find a Dremel and 20 cut off blades works well for tight quarters. I showed the process somewhere here one day.
Those walls. Which are yours and which are your neighbours? Remeber that multi family reno's you need fire rated processes - often fireboard is required behind backer board. So in your case you might need fire board, then your shower liner and then concrete board.
I would use a cast iron clamping drain. Watts makes one. Zurn has one. ACO makes one (and some great linear drains for across that back wall).
Make sure you understand firecodes for your walls and floor penetrations and make sure you remove that old plumbing. The process is difficult and takes me most times 1-3 hours depending on how steady my hand is and how big the through hole is. Hilti makes great fireproofing products for the repairs.