Many thanks to all of you. I have the exploded diagram that comes with the model but iy isn't very useful here - doesn't even show the screws that attach the clips to the chassis. My eyes are not as good as they were and I couldn't see the level of detail revealed in the posted photos of the bogie clips. I will get the magnifying glass out and give it a go.
Oh - I've tired wiggling things around to refit the shaft with the bodies in place - there doesn't seem to be enough free play though.