Don’t worry about a dihedral brace. Get some sheeting and make doubler ribs for the center ribs that can be sanded for the dihedral you want and a tight fit. After the wing is epoxied together, fiberglass the center section with 2” – 4” wide fiberglass. It’ll hold up to anything you can dish out to it. I’ve built many planes that have had the center section glass and no dihedral brace without any issues at all.

Hogflyer