Both the fuel line to engine compartment and the fuel tank (no cap) were open to the air for 3 decades. Suppose either would be easily the issue. I wish I had dropped it before putting 5 gallons of gas in it. Sometimes being in a hurry for no reason, slows you down longer that if just doing what you know you should have in the beginning.
Probably time for new lines. My 66 Dart tank looked like a cave inside with stalactites of rust even after cleaning. Time for a new tank and lines. I did that about 15 years ago with no issues since.