Jay, a 12 oz. Dubro square fuel tank is plenty large enough for a 26 cc engine. I have a 16 oz. tank in my 1/4 scale Cub (mounted crosswise behind the fire wall), I get 15 min. flying time on 8 to 10 oz. of fuel. The I use is 5/32 or 1/8" ID Tygon fuel line for gas engines and make sure you get a gas conversion stopper. These items can be found on Tower Hobbies web page. By mounting the tank crosswise, it can be completely hidden from the cockpit. The #2030 post on this page, is my Cub, Cub II is still flying.
Post some pictures of your Cub build, we all would like to see them.
Fair Winds & Happy Flyin'
Rich