I’m enlarging/changing an existing shower pan in a basement slab. The existing pan is several inches above the slab and incorporates a drain into a cast iron system. My new tile is thicker than the old, so something has to be done (e.g. replace the drain or reduce the pan thickness to accommodate the new tile and leave existing drain in place). Would like to replace the drain/strainer, but that isn’t a deal breaker. I’ll be pouring (adding to) a new pan to accommodate the new shower size. The existing drain has a classic cast iron (i.e. poured lead) fitting.

Comments/opinions on options, problems, or best way to approach this? I’ll hire a plumber to do work beyond my skill set.