I am building a 1939 Plymouth on a Chevy Nova frame with a 350 4 barrel rochester. I have put a fuel cell in the trunk and I am using a Holley red 97gph 7psi unregulated pump. Do I need to have a return line for the car or not. Its not for racing just for show.

Interesting that you are attempting to "return" this car to a condition that never existed in the past. You might find people more knowledgeable about that in other forums that are focused on "updating", "modifying" or "improving" cars rather than this one which is oriented toward restoration.

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restore |riˈstôr|
verb [ trans. ]
bring back (a previous right, practice, custom, or situation); reinstate : the government restored confidence in the housing market. See note at recover .
• return (someone or something) to a former condition, place, or position : the effort to restore him to office isn't working.
• repair or renovate (a building, work of art, vehicle, etc.) so as to return it to its original condition : the building has been lovingly restored.
• give (something previously stolen, taken away, or lost) back to the original owner or recipient : the government will restore land and property to those who lost it through confiscation.
DERIVATIVES
restorable adjective
restorer noun
ORIGIN Middle English : from Old French restorer, from Latin restaurare ‘rebuild, restore.’