I literally just used one of these a week or two ago for a very similar situation. Not replacing the tub, but had a nasty, leaky seal (in a 2nd floor, no less). Worked like a charm. Old guy a lowes told me to 'hit it real soft with a rubber mallet and use a long breaker bar with a torque adapter so you don't break the pipe'. Might not be necessary to 'not break the pipe' in your case, but in case someone else comes across this post in the future - if your crossbeams are broken, buy a crossthreaded remover like above. Works great!