My contractor tells me that is is ok to reuse the old bathtub drain assembly for a new right hand acrylic shower pan in a stand up shower. I have my doubts based upon reading the city code. Thoughts? Is this ever done?
I always use a new drain for a new tub or shower.
It may be that he's talking about the 1.5" trap and trap arm on the tub and the shower normally uses a 2" trap and drain.
There isn't much you can do there unless you have plenty of access to upsize. The shower will work with the 1.5" trap, just like it worked for the tub also.