Only, like, a gazillion cars don't have tachs from the factory. Manual transmissions even!

This one is pretty obvious. Get the cluster situation figured out.

Side note- I've had a bad oil temp sender before.

 

You know what I meant, obviously cars have been made without tachs. BUT they are in modern cars for a very good reason, I know when to shift without looking at the tach by the sound; but newer owners might not be and redlining your car is not so good for it.

 

I know when to shift by sound also I own 3 manual trans vehicles, and I have learned personally what over revving an engine can do! 1987 Toyota pickup with a 22r 4 speed with overdrive I over revved it starving rod bearing #4 of oil eventually causing the bearing to spin