Dan-
Hey, whats up?
If you are thinking of putting a gen 3 SHO speedo in your gen 4 forget it. I already tried. The 8k tach will work, but the speedo wont work. In fact, it wont even MOVE...and it wont plug right in to your gen 4 instrument cluster. The pins are different. I tried a couple different speedos from gen 3's in my gen 4 in fact, and NONE of them worked. One of them moved but only when I would start the car. Then it would jump up to 20MPH and stay there.
It would have to be custom. I believe it would have to be wired into your computer or ABS moduel because thats where it reads the speed from I believe. Lord knows how to do that...So, no, it is not "plug-n-play." The only cars the gen 3 "150" speedo will fit into with no modifications are the 1996-1999 Tauri and Sables.
-Kyle