Want to put and aftermarket tach in a rallye dash

I also have done 2 other things to take the devil out of the rallye dash. I did an ammeter bypass, , converted my ammeter to volts. And i bypassed the IVR in the fuel gage, and made a solid state IVR to attach to the back of the cluster. Notice how my ammeter looks like its on full discharge in my last pic. Its actually a volt gage with no power applied.