I guess that you have a mechanical engine-driven fuel pump, not an electric one. Without a gasket, the sediment bowl will leak air, and the pump would rather suck air than petrol all the way from the tank. If you had an electric pump, mounted near the tank, then I would have expected petrol to flood out of the bowl as soon as you switch the ignition on, hence my assumption that you have a mechanical pump (not uncommon in 1964). On one car I had many years ago (can't rember which) the pump had a lever on its underside which you could operate manually to prime the carbs without having to turn the engine over.
Hope this helps!
