That spring on the bulkhead looks to me like an economy device. I have never seen one, only seen a picture of it in a factory brochure. It has a bracket (bent out of the way there) that the lever on the cross rod comes against at about half throttle, so that full throttle requires a lot more foot pressure.
If I am right, you have there a real piece of rare Landrover history.
I should also point out that there is a missing spring on the pivot mounted on the body next to the manifold - the spring on the carburettor is probably to replace this. Also, it is likely that free play in the linkage between this point and the throttle arm on the carburettor may have a similar effect to loose engine mounts, so that engine movement can affect throttle opening.

