Seconding what Glen said, since the tail force is inverted you need anhedral to promote roll stability. Dihedral in a conventional tail is actually anti-stable and the Crusader design is just a bit whacked. It works because it's a high-wing configuration with the CG located well beneath the wing plane, which provides restoring force (kinda like the ultra forgiving Cessna), enough to overcome the tail's effect.
If you have a zero-dihedral biplane scissor with one wing above and one below, you lose the high-wing benefits and roll stability is gonna be pretty hard. Best hope is large tail volume and significant anhedral. If it shows a stall tip-drop you can play with sanding in some washout to reduce the angle of attack of the dropping wingtips.
A real wild hare idea (not original, i've seen this done) is to release a small weight on a boom that will swing down under the CG at ejection to move the CG downward. If you're sending the pod out the back you can arrange a release clip easily.