The gauge hood in my Miata has been scratched up since I bought it, but I knew there was a good chance it would break when I had to open it to replace my speedometer cable. After 25+ years of sun exposure the plastic gets very brittle. There are two main options for reproduction Miata gauge hoods. Those produced by Classic Gold (90-93 and 94-97), and the version made by RSpeed (90-93). The NA6 and NA8 hoods are not interchangeable.
Not much to explain except that it is very difficult to remove the old plastic gauge hood without cracking the brittle plastic. Screws fasten the hood from below near the steering column, and push-clips along the back insert into the dash. The force needed to pull out the clips similar to the amount needed to snap their plastic posts. A big chunk of the back snapped off when I removed it.
The Classic Gold replacement gauge hood has great fitment. The plastic texture is slightly smoother than OEM, and the color is a bit darker and shinier. Some of that is explained by the age of the OEM plastic. The new hood does not look out of place with the other original interior trim, just fresh.