The NB Sliver smoker and the NB Black Diamond are very similar as far as design. The Black Diamond had an optional warming plate while the Silver did not.
The main difference is age. The Silver Smoker was first introduced in 2001 several years after the acquisition by Charbroil. The Black Diamond dates back several years earlier.
A good rule of thumb is to try and find a New Braunfels smoker made before Charbroil shut down the New Braunfels manufacturing plant (Spring 2002). Manufacturing then switched to Georgia and ultimately China.
OK Joe's Longhorn & Vertical Roasting Oven, Brinkmann Cimmaron,'69,'73,'84,'89 Weber Kettle