I want to remodel an old bath and add a stand up shower in the process. I have no experience with cast iron but this is what info I have gather so far and want to know if I am in the right vicinity. I do not want to replace all the cast iron because I don't want to rupture the line and then have to replace it all the way to the street. I am thinking of cutting the cast iron as least 3 to 4 feet before the ptrap on the tub, come in with a fernco fastener -and run 2" pvc , then connect a tee(so I can veer off for my shower) run 2" pipe to a 2"in p-trap and then use a reducer(2" to 1 1/2") because the drain for the tub is 1 1/2 inches. Of course the stand up shower I am going to use 2" pvc, p-trap and drain. Just want to know if I am missing something( I probably am) Any help with this would be greatly appreciated.