The ribs were not badly distorted, but all were bowed, so needed to the "fluted" so that they lie flat and the rivet holes in the flanges are in a straight line.
I found the easiest way was to start fluting in the middle of a bowed edge and apply pressure with the fluting pliers to reduce the bow somewhat, perhaps by half. I then moved halfway left between the middle and the end and repeated the exercise. Same again with the right hand side. What little bow is left after three flutes can be eliminated by small flutes, as required, in the intervening spaces. The same technique on the opposite side resulted in the requisite flat ribs. After a handful of ribs the process became more intuitive and thereafter only took a couple of minutes per rib.
