Good luck with the restoration.
The first step to trouble shoot a fuel gauge not working is to locate the sender unit which is typically at the aft end of the fuel tank. There should be a way to access that spot. Usually there is a deck ( or pie) plate over that area. There should be two connections for the sender but for now we are looking for the signal wire. If Grady used their standard wire colors way back, the signal wire will be pink. unplug that wire at the tank sender. Your gauge should read empty. Now run a wire from a known good ground like the black battery terminal and touch it to the end of the disconnected pink wire. Wait a bit and see if the gauge moves. It should eventually read full.
If those two tests work, most likely your sender is bad ( likely) or the ground at the sender is bad. If nothing changes with the above tests, you will need to get to the back of the fuel gauge and look for the pink wire. One step at a time
On another note, I am not sure what remove the helm means. I have never seen a Hatteras so I can only go by what can find on the internet. Isn't that a cuddy cabin style of hull?
Can you post a photo of the helm area and the space behind the helm in the cabin.