Actually, the Cleveland was only offered in the US from 1970 to 1974...the 351M (sometimes thought to mean "modified", other times said to indicate "Midland", where the factory was located) and 400M were offered for a considerable time after that.
The "M" series had a higher deck height than the Cleveland. Intake manifolds do not interchange between the Cleveland and the "M" series, not sure about the cranks, but most everything else will.
From a purely power related point, you'd be much better off with the slighter smaller and slightly lighter Cleveland, but if you want to retain the originality you'll need to determine which motor the car has (almost surely one of the "M" series). The "M" series are making great strides, though, as more development occurs. They have recently scored very well in Popular Hot Rodding's "Engine Masters" competition.
Both the Cleveland and the "M" series were part of the Ford 335 family of engines:
Ford 335 engine - Wikipedia, the free encyclopedia
{edit....I just realized you're in AU....that's very different, you were lucky enough to have the Cleveland versions for much longer than we Americans had them.}
Cheers from Dugly!!
