Take the face plate and scan it on the flatbad scanner, then modify it. Finally, print a new one out with the photo printer. You can modify the font, colors, etc. Bolt it to the speedo using the standard screws.
Also see:
Raw Scans
Custom Files
Here is a multi-layer PNG file, which you can print out in a photo printer.
You could also modify it first (it is calibrated for 4.11 diff). Perhaps reverse the colors to black numerals on white face?