W116 instrument question

[Sid123]

Does anyone know what dictated whether a W116 had just a clock or a rev counter with a small clock in the same dial on the right handside of the instrument panel?
Most rhd 280s don't have a rev counter (although some do) and most 350s and 450s do (although some don't). All 6.9s have the rev counter so I wondered if there was some country spec or trim choice that made the difference?
Presumably if you don't have the rev counter one can easily be fitted to replace just the plain clock?
Any thoughts appreciated. Thanks

[Sid123]

Thank you