The steering rack is time consuming to change, you need to drop the sub-frame. So they got the working ends of a LHD and a RHD rack and stuck them together.
As yer know Mike, Minis were made to be either right or left hand drive....but not quickly convertible...
My Manton Question is: did they have two sets of clutch and brake masters plumbed in? swapped pedal box to waiting masters? Two pedal boxes? Two accelerator pedals? or some sort of linkage arrangement (unlikely) or quick release connections on the masters or geez Louise! run out of ideas
Swapping the pedal box and master cylinders from one side of the car can be done in about half an hour.
No need for quick connectors, from memory it is six nuts to remove the pedal box and just two hydraulic pipes to undo.