Here are two examples of fuel sending units for Mustangs. On the left is a sending unit for '65-'68 Mustangs with the factory 16-gallon tank. On the right is a sending unit for a '70 Mustang with a 22-gallon tank. Note the longer float arm for the 22-gallon tank. Truth is you can use the 16-gallon sender on a 22-gallon. It just stays on "Full" longer.