Never rely on the automatic shutoff when filling antique cars. You shouldn't do it with modern cars, either since sometimes the latch mechanism sticks.
The air in the tank being displaced by the gas being pumped in has to come out the filler neck on the tank on these ole rigs, modern rigs nozzle fits tighter to filler, air / fuel vapor enter the vapor (EVAP) canister, fuel vapors held.
Farmers can tell you about plugged EVAP canisters & fuel tanks sucked in.
