This has got to be the one of the most unusual dual locking systems I've seen, it was only after re-discovering it and deciding to make a couple of new keys that made me realise how different it is.
At 17 inches X 3.25 inches it's a fair size and weight- 12 inch rule shown for size. No markings except for a couple of numbers stamped here and there, and just in case we didn't know it's got 'dual control' stamped along the top of the salvage.
Click image for larger version. 

Name:	image.jpeg 
Views:	27 
Size:	1.39 MB 
ID:	17521 Click image for larger version. 

Name:	image.jpg 
Views:	26 
Size:	464.4 KB 
ID:	17522
The right-hand nozzle on the left, and the left-hand nozzle on the right are basically turnknobs- the right hand one releases the sprung hook bolt and the left hand one drives the main bolt lath to lock and unlock along the top.

Perhaps what makes it more unusual is that both the 6-lever locks, left and right have sprung 'latch' actions and not dead bolts, so both keys have to be turned and held in position against strong spring pressure at the same time the other functions are operated- also against strong Spring pressure- easier said than done, even with two operators!

The bar and stump visible at top right of the left-hand lock is a device actuated by a projection from the closing lid to prevent it from being slammed down when in the locked position. The bar and stump prevents the entire system from being closed to the locked position unless the sprung Bar is depressed down to effectively pass the stump.
Click image for larger version. 

Name:	image.jpg 
Views:	20 
Size:	425.7 KB 
ID:	17523 Click image for larger version. 

Name:	image.jpeg 
Views:	22 
Size:	1.16 MB 
ID:	17524