Hi,
Yes it's possible to do both. i did on my 63 c10. You will just use the factory wiring harness for the dash idiot lights. For the temperature idiot light, i used the factory harness and connected it to the factory sensor, but used it on top of the intake, because i didn't really care about the light going on from that point. For the aftermarket temp gauge, i used a mechanical gauge and ran it through a factory hole in the firewall and have it coming directly from the engine block. Usually mechanical gauges have the temp sending unit on it. I used a "Stewart Warner" one.
For the gen light, it just uses the factory harness for the light to go on.
For the oil pressure, same thing. I ran a Stewart warner gauge and put the line through the firewall and directly in a port behind the distributor for oil pressure. Reads great too.
So, yes you can do both. I'm assuming you can do electrical gauges, but it's all wiring and maybe more of a voltage sensor, where mechanical gauges give you a true read out.
Hope this helps.