No one in this hobby needs to own an alligator gar they can get up to 10 foot long. They belong in the wild or public aquariums. Don't even consider buying one a needle nose gar is doable but requires a huge tank they can still get 24-28 inches. In the wild they can get around 3 foot. If you want a needlenose go buy a 220 gallon 8 foot tank for them.
It depends if its a 30 foot by 30 foot tank maybe maybe you could keep one still its a huge fish.