We are redoing the master shower in our newly moved into 1964 built house thanks to a shower pan leak. We've already ripped up everything down to the slab and have come across this drain flange that I don't know what to do with. We are planning to use a "ShowerSlope" by Custom Building Products for the pan and it is supposed to come with a new drain assembly but I believe the existing drain pipe is too tall for it to be flush. What needs to be done to the old drain so that the new one will fit with our pan and not leak? I have attached photos of what we're dealing with. Any help or advice would be greatly appreciated. We are a fairly decent DIY couple so if we can do this ourselves it would really help our already surpassed budget. Thanks!