The large white-ish roughly cylindrical object is a full size polystyrene model of the wfcam cryostat.

The circular UFO-like object on top of the grey stand is the “spare” mirror plug – which has an identical wfcam interface as the one on the telescope. The grey stand supports the spare mirror plug the same height above the ground as the real mirror plug is above the dome floor. 

Photos by Brad Cavanagh