The sending unit gasket is included. Originally the 47-55 1st series trucks used a fuel sender which did not have a fuel pickup.  The original 47-55 1st series trucks were gravity fed and the fuel line attached at the bottom of the tank. If you are using this sender in an original 47-55 1st series truck and continue to use the gravity fed fuel line, use the brass threaded plug (enclosed) to block off the top on the fuel sender feed.

No modifications necessary for the 55-59 series trucks.