Final-fitted the fiberglass cap on the rear seat-back: Trimmed off about 3/8" of cap in accordance with plans. Filed and Dremeled various areas to improve the fit. Marked and center-punched rivet locations on seat. Clamped fiberglass cap in position. Finished fabricating small side stiffener pieces and drilled/clecoed them in place. Match-drilled cap and seat-back to #40 size. Removed fiberglass cap. Finished fabricating top aluminum stiffener angle, clamped it to seat and match-drilled it to existing holes. Reassembled all pieces and final-drilled them all to #30.