Fuel Gauge Issue

Need some input. I have 1968 Satellite converted to 440 RoadRunner Clone. Car has new fuel tank and sending unit in gas tank. Wires from sending unit to fuel gauge checked and find to be good. Only owned the car few month. Original owner who did conversion said the gauge was working. Other than something being wrong with the gauge, any suggestion on what I may do to fix the issue. Really not crazy driving around with not fuel gauge.
Appreciate any input on this issue.

Yeah, carry a 5-gal gas can for a little while + a funnel with a long snout. What is the gage doing or not doing?

If the gage stays on "all the way empty", AND you've verified the wire from the sending unit to the gage is good (continuity) then do this. Un-hook the wire at the sending unit & connect it to a verified good ground with a jumper wire. Turn key to "on". If gage & circuit board are good, the gage will go to "all the way full" in a minute or two (gage responds slowly). If the gage is still pegged empty, then your problem is a)the gage b)the circuit board behind the dash or c)some piece of wire is broken that you missed between sending unit & gage (not too likely based on what you said). Oops...I forgot d)you don't have power going to the gage. Is your oil pressure & temperature gage working?

Now, if the gage did peg full when you grounded the sender wire & key on, then your problem is either a) the sending unit in the tank or b) missing/bad ground strap that goes between steel sender fuel outlet nipple and steel fuel line (jumps ground over small section of rubber hose near sender).

Is there a metal clip connecting the fuel tank to the fuel line? This metal piece is about 2 inches long and has 2 "U" shaped clips that clip onto the metal fuel lines grounding the system.

(I need one as well on my car.)

You really do need the ground clip & it needs a clean ground. If the gauge reads E pull the sending unit. On my street '70 Barracuda the gauge quit working, so just knew about how many miles I'd get from general driving. Ran out of gas in Northern Minnesota country road. Decided to fix it. Turned out when I pulled the sending unit out, with very careful inspection I could see the reostat winding was broken. New sending unit, cleaned up ground, all good.