Mike

I did exactly the same repair on mine. Problem is the U/C plate has tongues on both ends for assembly with the formers and not after! I made up a 6mm ply plate with a tongue on othe front end, drilled for and fitted the blind nuts, got that in position and glued a 6mm ply plate about 1/2" deep to the undersride of the U/C plate and to the front of the rear former. Replaced the 1/4" square stringers and sheeted with 1/16" balsa, sand/fill and recover, good as new and I suspect stronger.

regards

John