Just to clarify my expertise......I am NO expert in this matter just another bloke with another opinion.
I believe the split was very much a success and kudos must go to the organizers.
I agree with Slakewell. If a bike was manufactured before 12/1977 and happens to have a bit more wheel than others in the era, I don't see why it the bike should need to modified "backwards" to conform with a rule book. The rule regarding eligibility should be as simple as " a bike manufactured ON or BEFORE 12/1977 to be eligible for Pre78 classes. Any bike outside of the standard ruling regarding suspension (wheel) travel must have proof of same in the form of brochures or magazine article from the day. Actually, to the best of my understanding, If you can provide documentry evidence that the bike came from the factory and or custom frame builder (C&J, Al Baker, White Bros etc.) with the extra travel, then it must be considered eligible.
As for the pre78 cut off date, if you take a good look at bikes available between 1975 and 1977, they do fall short in the suspension department compared to 1978 bikes where nearly 11 inches of travel was the norm.
In saying all this, I personally believe that Australian VMX rules should follow what is happening in Europe and the US where they have different cut off dates than we do. We only have to look at the size of the race meetings and all the beautiful exotic machinery they get to see that Aussie VMX is missing out on something....