Long tanks are better for goldfish because it means a greater surface area for gas exchange. Long tanks are just better in general for fish. I know the size tank you are talking about. It's typically sold as a 30 gal breeder. Not a common tank.
As for whether or not a goldfish can live in one, with a sufficient filter, I think it has the space for one, but goldfish are social creatures. They can live alone but prefer the company of other goldfish, but that tank is physically too small for another goldfish. You would also be restricted to the generally smaller breeds of goldfish. Oranda and black moore are notorious for getting really large. Ryukin and pearlscales tend to stay smaller. What breed were you thinking about getting?