A '76 should already have a 1/4" fitting at the front upper right corner of the tank that was originally used as a vapor return line from the charcoal cannister. Plumb your return line in there.
STop telliing people this WITHOUT explaining. YOU CAN NOT USE that line UNLESS you do something "else" about fuel vent. THAT 1/4" LINE IS THE FUEL TANK VENT!!!
If you want to use that existing 1/4" line you have a couple of choices
1...Look the 69/ earlier, simple, vent line into the filler neck. Modify the neck and create that style vent.
2...Use a vented cap (The stock cap IS NOT vented, it is, rather a pressure relief "pressure vacuum" cap, that relieves excess pressure, either positive pressure or vacuum pressure in the tank.) I do not care for that solution, as the filler necks are all rather special and it may be difficult to even GET a vented cap, plus, you run the risk of fuel spills out on the quarter panel.