My cruiser has oil, fuel, water temp, and volt built into the factory gauge cluster as well... but I am going to add the Autometer water temp and oil pressure gauges just so I can actually get a reading rather than a line indicator. I added the Sport Comp gauges to my last cruiser and never regretted have two sets of "eyes and ears" watching my motor.
I sell alot of gauges to folks that already have their stock ones... not sure about your application but some of the factory gauges are actually operated on just a switch, not a resistance sensor. Meaning: they don't actually indicate the exact pressure, temp, etc...
Options for gauges:
Tach
Fuel level
Oil Pressure
Water Temp
Volt
Fuel Pressure
Boost
Vac
Oil Temp
Ammeter
Clock
Cylinder Head Temp
EGT
Trans temp
Air/Fuel Ratio
Pyrometer