If you can't get them apart, and there is a substantial plywood dihedral joiner in there, I would suggest that you fiberglass the center section with fairly heavy glass (like 6 oz.) and slow dry epoxy. Then fly it. Many of the older "jet style" pattern planes relied on only the glassed center to hold the two halves together and they held up to high speeds and pretty high "G" forces.

Clair Sieverling