Help me understand the fuel system!

Back in the 80s I ran a Cadillac PFI pump with a homemade brass T bypass regulator that returned into the filler neck. I kept line pressure to the Holley regulator up front at about 20 PSI and regulated it to 8 PSI to the carbs. It had 5/16 line and still fed a 440 Six Pack through the 1/4 mile.