Seems that there is a bit of confusion and misunderstanding going on in this thread... I hope I can help get this settled. The speedometer faceplate that 48hp has replicated looks exactly the same as the one I have which was purchased in Europe 6-7 years back. That same style speedometer faceplate has been found on several members cars in the US all of whom I know have AMG-modified components. Eurocoupe's old 6.0 32v SEC, JonWhite's 5.4, a red Hammer in the US, a black Hammer in the US, a silver Hammer in the US came with the exact faceplate as the one 48hp has replicated. The RHD Hammer that belonged to Vlad in the UK and was sold a few years back had the same style but in a different color combination.
I also noted in some 1986 and 1987 catalogs where it showed W124's with the same style AMG speedometers. So as to authenticity, I am fairly sure they were produced this way back when they were being made.
As to Talbir's speedometer style, I've seen one other car with the same faceplate. I have no doubts that his is also authentic, especially with the car's pedigree and history.
The MPH speedometer faceplate posted by mapearso looks strange, and I've never seen any other car with a similar speedometer. It could have been made in the US by an outsourced place that AMG of NA contacted... but its not a usual faceplate if its infact a genuine period correct piece. Speedometers from different regions of the world can differ as fonts can vary. I noted that the 300 and 320kmh speedometers on Japan-spec AMG's can differ from ones that are in Europe. It could be that AMG Japan simply had their own shops that produced faceplates. Not saying that mapearso's example is not genuine, but its certainly not a usual piece and certainly not seen in any literature that I've got or 1000's of pictures I've collected.