An oval would be considered an ellipse. A semi-ellipse would be the equivalent of half the oval, for this example lets say the lower half. That basically what most leaf springs, front or rear, are on cars and trucks. Your F1 should already have semi-elliptical springs on the front if it's stock (as well as the back).

Now that we've dealt with terminology, how do you lower it? You can go to a spring manufacturing/repair company, most good size towns have one (they do a lot of work for HD trucks, so check with one of those type shops if you can't find one in the phone book) and have them make you a reversed eye and/or de-arched set of springs, or you can get a pair of mono-leaf springs from Durant Ent. 949-673-5625 (no website listed)