121mm Super Angulon

I have just got a 121mm S.A. mounted to a Plaubel lens panel.
The lens appears to be fitted into some kind of housing which has larger
rings for the shutter speeds.

However it looks like there is normal Compur shutter mounted into the
housing, yet I cannot remove the lens cells and shutter from the housing.
Normally one has the shutter,you remove both cells to fit into a lens panel.
When you have tightened the locking ring only then you fit the cells of the
lens.
This thing has a flange which screws tothe lens panel by three screws and
the housing screws to that..