You will need the return line to the fuel tank. In the conversion section there is a write-up on how to convert the OBS trucks to an LS1. Within the writing is a description on how to handle the fuel filter and supply lines. I don't do anything with the fuel tank vent hose except hook it directly to the brass fitting on the driver side of the throttle body when I go for vehicle inspections. Afterwards I disconnect it and cap the TB fitting and vent the fumes to the atmosphere.