There should be a slot in the fuse ready to accept the fin. Mine did. Yours doesn't so you need to make do with what ya got. You could try to cut your own slot, but as I recall it was deep, so you could make yours shallower and cut some of the bottom of the fin off. You can determine how much by holding the rudder in place to see how much fin needs to get buried. Another option is to cut the fin flush with the top of the fuse, and then use the largest dowels that fit in the fin thickness, perhaps 3/16" diameter. Use two or three dowels, maybe 1.5" long, and drill holes about 3/4" deep in the fin and fuse. Make sure you get the fin as vertical as you can, easier said than done in this case. There are other ways to skin this cat, but go for it because this plane is a lot of fun to fly! It can groove around like a decent pattern plane, or you can fun fly it. Mine has an OS 70 Surpass II which seems to be a perfect match. Good luck, Jon