I have a 1968 coupe.
You need to get the nozzle as deep as possible into the tank and fill it slowly. Otherwise it will splash back out at you
I usually hold the nozzle sideways and pull the rubber back to get it deep into the gas tank.
I think the gas nozzles of the '60's were more curved, pumped slower, an went deeper in the tank.
Plus I never let full service people do it, they always spill