Well done Skytrain, Good Challenge Graeme! Glad it's all sorted, just like my neighbour's drains!
LM, it was precisely because very few aircraft of that period had L/E Slats that I thought it may be a significant clue, I had ruled out the discontinuity being due the the flaps showing, as they spanned too much to allow for the aeilerons.
Now that I've had a chance for another and closer look, I think that they are probably an artefact of light/shade on panel lines which may have fooled the silhouetting process (and me
) plus the fact that they appeared to go right over the gun-ports too
!!