We are in the process of purchasing a condo in Cambridge MA. The bathroom currently has a free standing cast iron tub with feet. The current owner has surrounded the tub with shower curtains and affixed a make-shift shower head above the tub. Our current plan is to remove the (very heavy) tub and replace with acrylic style shower/tub unit. Will I have to remove the plaster walls inorder to properly frame in the fixture or can I simpley frame in the new unit and leave the plaster walls in tact, saving a large quantity of work?