There's one thing I don't understand...
I have proved with these diagrams that the engine is NO LOWER AT ALL. Yet each time I have stated that someone comes back and says it's lower. It definitely is no lower!
The cylinder head casting, in fact, is higher with the engine slanted. Look closely at the diagrams.
The lower centre of gravity is principally because the camshaft and lifters are significantly lower and the right side of the engine is lower. The left side of the engine is higher. A further lowering of the centre of gravity could have been achieved by the retention of an alloy intake manifold, even more with an alloy head.
Yes, the engine bay in the Australian cars was the same as US cars until 1969, the only differences being in the chassis rails where the steering box and idler arm are mounted.
As to engine length, the shortness of the engine relied on two things. First, the bore centres being close together; second the water pump being mounted to one side. BOTH of these could have been achieved with a vertical engine.
The engines sat no lower in the Australian cars, they didn't have to. The suspensions were no lower, that would never work here.