My recommendation is similar to Carl's but less steps.
Fit the flaps and match drill the holes in the hinge.
Remove the fwd hinge half from the flaps.
Cut some .032 thick strips (preferable on a metal shear so that they are straight and flat) the same length and width as the flange on the hinge.
Match drill the doubler strip using the hinge.
Machine countersink the hinge
Rivet together with the hinge sandwiched between flap brace and the doubler strip.
Any opinions expressed in this message are my own and not necessarily those of my employer.
RV-6A (aka "Junkyard Special ")