`There are less expensive ones listed by other vendors that look the same. http://www.tanksinc.com/index.cfm/page/ptype=product/product_id=260/prd260.htm
All the p***enger cars use the same tank... except for the wagon/sedan delivery. Capacity is 17 gallons for cars, 19 for the wagons (as per the Ford owners manual).
For what it is worth, here are some photos of the gas tank on the restored 1956 Sunliner Convertible I am selling. It appears to be a new gas tank. I am not sure what the capacity is.
All '55 and '56 Ford cars except wagons and sedan deliveries use the same tank. The reason for a different tank on wagons and sedan deliveries is the filler location. Wagons and sedan deliveries have the filler in the left quarter panel, all other models have it behind the license plate.