90% of the oil gauges I've seen have just never worked, I'm not really sure what the issue is. Some seem to work okay.
The temp gauge will run up 3/4 or more on the scale, this is normal.
If you want to add aftermarket gauges, you'll have to find the correct adapters or fittings to screw into the block. You could use the thermostat housing for the coolant, and add a Tee or just replace the oil pressure sender.
RC - I don't think they don't lose calibration, they're just crap gauges to begin with. Thats why ford switched to the High-Low style, because of customer complaints about the guages running way off what they consider "normal" on the scale.