They aren’t CO, the cases are larger at the rear. The Post War CO was assembled from left over WD/CO parts and the very last COs used C crank cases with CO cylinders. If yours were one of these, you’d have a Model CO serial number on the front of the case and if I remember correctly, new drain holes like the CO case. It could of course have been a non factory modification that someone has later ‘undone’ and not realised what the hole was originally for.