Hi Mark,
The access hatch needs to come off to gain access to the fuel line. 20 or so screws, cut the caulk and lift off the hatch. Most fuel tanks corrode from the outside in from water being trapped under the tank or laying on top of the tank if the hatch isn't sealed properly or the caulk is dried up and shrunk over time. The tank needs to come out and be inspected. It's probably contaminated with varnish if it had 40 year old fuel in it. This may include having to remove the console to lift out the tank but it depends if the cut out at the bottom of the console allows enough clearance to lift up the tank on one end and pull it out. The cooler seat will need to come out also. Having done this myself I would say 10-15 hours of labor is what it will take to do this. The steering cable is not a bad job as long as the engine does not need to be removed to pull the cable end out of the engine. The only overlap in labor savings between the fuel tank and steering cable jobs is removal of the access panel that runs down the starboard side of the boat that needs to be removed for either job so that's only about 15 minutes. Not knowing what your dealer hourly rate is and if your tank is in good usable condition you are probably looking at $750 to get both jobs done.if the boat has been stored inside during its life and has a solid floor, transom and nice gelcoat then it's worth doing these jobs, if the hull and engine need work sell it as is.