The age of the coach has nothing to do with it. The same or similar 4" center fittings used today have been used for many, many years in RV's.
RV Shower Faucets at AmazonThe Dura Faucet listed first is the one we used as a replacement in our 1995 Coachmen Catalina.
For a shower head, we like this one from Camco, but there are a number of others readily available as well. It has a "no dribble" shut off...
Camco 43712 RV Shower Head with On/Off Switch