Need help with this vacuum reading

Go with the cam red suggested or a Lunati 60401. Both will work with what you presently have. You won't really hurt anything driving it the way it sits. Your mileage will be much, much better with the aforementioned cams.

The rear end can be eyeballed by jacking up the rear and turning the rear tire until you have one driveshaft revolution. Just count the number of turns and fraction of turns. If you turn the tire 2 and 3/4 turns it's a 2.76 rear gear.