On a side note, member 70shortfleet can modify your tins to work with a factory-style tachometer. This involves cutting a hole in the back tin and cutting and forming a lip on the front tin.
https://67-72chevytrucks.com/vboard/...d.php?t=792563
Here's how I do these modifications for the gauge clusters I build:
https://youtube.com/shorts/0GzBrGi_a0Y?feature=shared
https://youtube.com/shorts/rUqBiEJ99aU?feature=shared
https://youtube.com/shorts/QPzylsrfP-w?feature=shared