Yet another view of the NA-2 port. The mounted instrument's weight is held by the two round posts at 3 o'clock and 9 o'clock, the latches at 2, 4, 8, and 10 o'clock hold the instrument tight against the flat rotater. The electronics include a guide camera that helps the telescope to track properly.
This is an older design circa 2005 and looks a bit different now. The round dark hole is the light path from the tertiary mirror.