i recently did the 85 - 140mph swap and this is my advise:
if you like a stock apearance in any way shape or form, DO NOT.
I have a GT, so when i swapped i lost my neat little lights that go to the right of the stearing wheel. Also, you have to get the wiring EXACTLY RIGHT, or you will trace an alternator problem for 2 weeks, just to find its behind the dash. Also the bottom bezel doesd not line up with the interior, in other words, you can see the inwards of the das uner the cluster. kinda annoying.
i would put my stock one back in, but i like to know how fast i am going.
your call.
Wiring diagram