I once had some replica clocks for the CB750 that were new and certainly looked the part. They were bought to fit during "down time" whilst the originals were sent to be refurbished. However, the replica tacho showed a higher red line than the ND unit and, when fitted I found that it over read by 50% or more compared to the original unit.
I removed the replicas from the bike and refitted the originals (still not refurbished) and things returned to normal again.
I still have the replicas in the garage in their original boxes, though I did remove the case from the tacho to decide whether I could fit new faces to my originals myself in the garage (I eventually thought that it was beyond my ability to make a decent job of this).
If anyone wants to collect them from Norfolk, the replicas are available free of charge.