I had a similiar problem when I changed my guages a couple of years ago. For the tach you could find out what your engine idles at and put the tach needle back on aiming at the correct RPM when it's idleing. You could also drive beside someone with an accurate speedometer and have a passenger that is riding with you put the speedometer needle on pointing to the correct speed. For the fuel guage, fill up the tank and just put the fuel needle on showing full. As for the oil pressure, battery, and water temp. try to put those back where you remember them to be under normal conditions. OR you could just forget about that cluster and upgrade to new completely different cluster(escalade/denali) with a tranny temp guage and 120mph speedo.