The primary reason for closing the eyes and placing the chin on the chest was to purposfully introduce a mild form of spacial disorientation
Well,well,well. That's a new one out of the box. Instructors did this fifty years ago on Chipmunks and even in DC3's. While spacial disorientation has been around since aeroplanes first flew in clouds, I can assure you Sheppey was right when he stated the original reason for heads down arse up with eyes closed was to discourage student pilots from looking outside and recovering half visual half instruments. I think its called corporate history
Purposeful attempts to specifically induce spacial disorientation was never part of the exercise although spinning on limited panel `under the hood` was part of the military training syllabus and this certainly could cause disorientation . In any case what is the point of attempting to give the pilot spacial disorientation in current jet transport simulators by making him go chin on chest and close eyes when the G forces involved cannot be replicated...