The RTE replacement board is $100. If you find a stock tach in any kind of reasonable condition for under $200 you’re doing really well. Most are north of $100 for something you will then have to pay several hundred dollars to rebuild.
The repops aren’t great. I wouldn’t buy another one. The screen printing is fairly low resolution, the construction is cheap and the tach itself is inaccurate. And they’re like $250 for that. I bought one used, wasn’t that happy with it right out of the box, and after using it for a couple years it started randomly bouncing the needle all over the place.
The pictures Mat posted are mine, I bought an SW 3 3/8” tach and pulled it apart. I cut the housing it came in down and fit it into the stock gauge cluster. I then used the block off plate out of the original cluster and cut it down to make a mounting ring. In retrospect, I would just make up some little 90 degree mounting tabs. Cutting the ring down and sanding it and fitting it was unnecessarily time consuming.
Anyway, I fit the 3 3/8” tach into the stock rally gauge cluster without modifying the stock gauge cluster at all. All the mods were to the aftermarket tach, which was like $150. So far it works great! It looks a lot better in my car than it did in that spare bezel I had laying around for the picture, that was just an extra I used to do the fitting.