We will assume an elec gauge.
I would put the sender in the stock sender's location (driver side lower intake - front). Relocate your stock sender to the thermostat housing (you can buy an FRPP chrome housing for ~ 25 bucks, or a cast piece from DAP or AZ for 10 bucks).
Seems to me that the dash clock is dimmed, which should mean that the dimmer circuit runs a wire up there. You can use that wire for your gauge's lighting, if you choose. Put a test light on the wire and run the dimmer up and down - you should see the test light dim and brighten as you turn the rheostat.
I dont know what else is on the clock's power circuit, but you might be able to use the key-on power to the clock for your guage (gauge's dont draw hardly anything). You can also source power and/or lighting from behind the the radio/HVAC console.
That is the big stuff I can think of. Good luck.