How interchangeable are 318 harmonic balancers?

James Clews said
I am not sure when Chrysler Australia changed the engines but by VH they were late but the VG model had a lot of hybrid parts in them

That's exactly what I've been finding as well, but not only for engine components. The majority of the engine compartment seems to be straight out of Detroit (so far), while the electronics (gauges, senders, etc) were supplied by VDO, and don't use the same resistance values as US vehicles.

I either pity anyone who does a concourse restoration on one of these, or have immense respect for them.

James Clews said
P.S. the early engines timing cover did not have a cast in timing mark but had a bolt on timing tag on it!

Thank goodness this is a "late" vehicle, as I can't tell you how many bolt-on timing marker pointers I've misplaced for my Fords over the years!