[DavidG]

All of the bodies with four doors have basically the same challenge when attaching the front of the upholstery quarter panel as the upholstery panel has to bend around the wheelhouse. If the wood is good then perhaps the density of the cardboard foundation isn't sufficient to hold the heads of the nails, which I've never encountered with LeBaron Bonney foundation cardboard. That's no help to you, however. Two possibilities would be to steam the back of the cardboard where it needs to be bent and curve it enough to relieve the strain on the nails so that they don't pull through and/or peel back the glued-down outer fabric along the edge and install tacks with larger heads into the cardboard, reattach the outer fabric and using a small block of clean, flat, and smooth hardwood against the fabric to prevent damage from the larger tack heads, drive the tacks into the wood.