Rather than try to nail the ribs to spars after the epoxy resin has been applied, I put the nails in first and then lined each numbered rib up along the main spar and just tapped the nails in part way giving due consideration to where the 0.8mm plywood leading edge would end up butting against the top and bottom of each rib. This creates a precise guide when covering both the spar uprights and rib faces with epoxy resin and bringing the surfaces together. The nails re-enter the previous holes and are then driven fully home.