I have just ripped out my old tub with tile walls (tiles were falling off due to lack of greenboard) and have put in the tub part of my new 2-piece fiberglass shower unit. Now I notice that the existing manifold and valve stems do not extend the extra 1-1/2" to where my new walls are. The fiberglass walls are 2" away from the studs, and my valve stems reach 2-1/2", so there's no room for the finished (chrome) collars.
What are my options? I have tried to get replacement valve stems at local hardware stores, but no one carries the Kohler fine threaded valve bodies to screw into my manifold. The only options I see now are to replace the manifold (ick!) or extend it by cutting it out and piping it up and out to meet up with my new walls.