1976 Dart Overheating and other issues

Timing. If everything is factory, then follow the factory guidance. The advance curve in a '76 distributor very well may be difference than a '75 and most certainly different than a '67.
The best source of information will be the sticker(s) in the engine bay. Clean them gently. Hopefully they are there and readable. One should have the timing. It will also show what rpm the timing should be measured. Use a golf tee to plug the vacuum hose that normally connects to the distributor.

While there, make sure the vacuum hose from the distributor to the timing port on the carb is not cracked or leaking. They generally last a long time but good to check.

lemme also mention that 1976 has a fair number of differeces from other years. Generalizations that may be often true do not always apply. Be careful when reading/hearing any sweeping statements about parts or systems.