A lot of this is supposition based on a SBWR-5000 light at the Indiana Transportation Museum - which was missing the MOTOR, GEARBOX, and LINKAGES at the time the photos were taken. I have tried to put together what looks like - what should be as far as mounting of these parts based on other lights.
Projection (A) is seen in next URL also. It is structure on the outer oval ring to which one of the rods from the gearbox is attached.