No, you do not need a return line back to the tank with a carbureted car under normal conditions.
Perhaps the little dial with numbers is a fuel pressure regulator. These are sometimes required when using an aftermarket fuel pump that produces too much pressure to the carbs. Often, too much pressure causes the fuel bowls to overflow.
I have SU HIF carbs on my converted injected engine and have that type of set-up and have dialed my fuel pressure down to only about 1.5 psi without any starvation issues.
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Tom - '60 544, '68 220S, '70 145S, '86 745T, '06 Mazda MPV
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