The hard fuel line dose not thread directly into the tank
Depending on how you decide to run your line you will need a fuel hose just off the hard line
...link... The early AD's use a shut off valve on the bottom of the tanks. The fittings on the valve make the transition from inverted flair to pipe.
You need a hose because the cab flexes
The proper sending unit and hose for your year will get you there.
If you do go with and under tank set up you will need the valve
...pic... ...pic... and/or this hose
...link...
