I believe that the 5500 rpm red-line applied to SS-350 and all 396 except the 375 hp version. However, one referance I have refers to some SS-350's having 5K red-lines.
I had my clock replaced 11 years ago. It was about $150. A good spedometer repair shop should be able to perform this service. Maybe they will sell you the movement? I think I remember seeing something in Hemmings about a generic quartz movement.