I've done a couple of older cars, fitted after market gauges, for a speedo, tacho, fuel, temp, oil and volts your looking at about $800.00.
VR's rely on the there own speedo for a pulse to the ECM, and trying to find an after market fuel gauge to match the sender could be hard.
It would look awesome, the ones I have done look great, I'm doing an old XT Falcon ute at the moment with VDO gauges (very reliable and accurate).
I think you'll have to do your homework, If your really keen there are ways around these things.
Let me know if I can help you anymore.
speedotom