Maybe I am misunderstanding this but is this welded bolt on the bottom of the tank? According to my experience on my 53 the hole on the bottom is simply a drain. The outlet should be on top where the sender goes. The sender has a pickup attached to it and the flexible line runs down in front of the tank thru a grommet in the floor and hooks up to the hard line. In the Chevy assembly Manual (green book) there is a drawing of this set up.
