Nice write-up.
A couple suggestions I have from when I installed mine. It was recommended to me that you start the car and let it come up to temperature before starting the installation. Mark where all the needles are, while the car is running and up to temperature, except for the speedometer and the tach.
After you remove the clear cover, slightly bend the speedometer and tach needle up and over the lower stop point. Do this while the gauge is sitting face up on a level surface. This will allow the springs in the gauges to "relax" to their unwound state. Mark this on the housing somewhere out of the way. Then push the needle up to the stop again and let go. Allow it to relax again and mark that spot. Do that a couple times until you get an average of where the needle falls when it relaxes.
The needles can be removed easily with 2 spoons, one on each side. It provides a smooth surface so you don't scratch anything.
When you reinstall the needles, just line up the speedometer and tach with the lines from before. Then hook up the cluster to the car again. You don't have to reinstall everything since you'll need to take it out again. Warm up the car and install the accessory needles when the car is running. Just line them up with the marks you wrote down earlier.
That's how I did mine.