Why not swap the entire cluster? Feel like I’m missing something here, lol. My choptop didn’t have a tach, I found a Ranger in the junkyard with a tach and the same style cluster and just swapped the entire thing. Had to swap the gear indicator for the block off plate, but it was easy as you please.
If you don't care about keeping the original odometer, you can skip most of that... it'll just bolt in, just might have some extra lights... You do have to use the tach cluster assembly, the gauge card is different and so is the lens. It's possible to keep the original odometer so I went for it.
And no, you don't have to do anything to make the tach work, the truck is already wired for it, other than being a pain to get to on the third gen dash it's not hard. To get to the cluster:
-pull two screws under the stereo then pop the stereo panel out (it just pops in, just find an edge you can pull and pull...)
-Pull the two screws that hold the hood latch up and the other 4 screws that hold the lower panel on then pop it off, it pulls straight back
-pull the bolts that hold the metal plate on under that
-pull the screws that that plate revealed and the ones that you can see just over the speedo. pull that stuff off then you get to the cluster