I go to NAPA...
and I get a new Stewart-Warner gauge, comes with a universal design sender. The sender is both height-and sweep-adjustable for any depth tank from about 5" to 24"... just follow the chart that comes with the unit. I used one of these senders minus the top plate for the 'sledd tank, there's a single mount stud/contact that holds the whole thing in place.
In the Cavalier 4x4 project I gutted the sender out of the original gas tank, and with a new plate fabbed up, adapted the unit to the stock '54 Ford 12 gallon tank, mounted where the spare tire well used to be under the trunk floor. The stock spare tire well was cut out and replaced with 16 Ga sheet., and I made the straps from 1/8" strip stock (shear tailings) from my local steel supplier.
With the tank turned sideways the Ford filler neck was aimed for the GM fuel door in the passenger quarter, but was obstructed by the floor/shock tower. I cut out the offending metal, and made a tunnel to weld in to cover the filler tube.