What are my options for increasing the fuel capacity of my 1978 Mustang II?

[@SPAZALOT]

the 78 Mustang ll I am building my son I cut out the rear spare tire well and surrounding floor, fabricated a square frame with 2"x2" square mild steel tube to fit between the rear frame rails, welded that in and bought a 1967/68 Mercury Cougar gas tank to fit in that opening, also used a 2 1/2" hole saw to cut out for the fill tube to go behind a 67/68 cougar pull down license plate holder and fill neck tube, hole in driver rear quarter is deleted, cougar tank is 16 gallons, mustang ll tank is 13 gallons

[@SPAZALOT]

you can even upgrade to a 69/70 cougar gas tank with 22 gallons

[@SPAZALOT]

Chassis connectors