[Stocker]

My saddle tanks (Travel Tanks, long out of business) have sending units in them. With luck maybe you can locate some. Just wanted to let you know they exist. Mine are wired to the factory fuel gauge through a 3-way toggle at the bottom of the dash.

Plumbing them might be a bit tricky. Maybe a large hose/tube connecting the bottom of the tanks, with a smaller vent tube connecting the top of the tanks. If you don't know for sure how to do it yourself, you'll need someone that can safely weld on fuel tanks.