Depending on the type of lungfish you get....certain Australlian lungs can reach 3.5ft....the SA lungfish a touch over 4ft and yes the larger ones can obtain upwards of 6ft+. IME the most common aquarium kept lung is the SA lungfish Lepidosiren paradoxa. This species being fairly eel-like and inactive could get away with an 8ft tank with a 36" width. Provide the tank with a bed of sand and some cover for the lung to hide away in. Also filling the tank only about halfway and fitting the top with a screen cover is the best way to house a lung...as they MUST have access to surface air and are prone to escaping the aquarium. Heavy canister filtration with a very low current is the best filtration options. They will eat practically anything, from chopped seafood to maybe even dried sinking pelleted food. They are said to become fairly pet like in old age, unfortunatly Lung fish of any sort really make poor aquarium pets and are not long lived in the tank.
150G SA Cichlids|100G Planted Community|50G Reef|20G Tanganyikan|10G Divided Bettas|10G Nano Fish
Common decency...imagine the nerve!