Here were my suggestions last time this came up:
The fixes are relatively easy:
1. List the parts that are considered to be major components (ie: the bits that define the bike as being of its era - frames, engine cases and forks vs lever assemblies, tyres and rims);
2. Re-format it so that the later classes are not just 'add-ons' to the original pre-75 classes. This can be done either by listing the common-to-all-era rules at the start and then have separate sub-sections for the individual eras' specific rules, or by incorporating them into the original format;
3. Make a blanket statement that either says "No modifications to major components are allowed unless permitted by these regs" or "Any modification is allowed unless otherwise prohibited by these regs". Ka-pow, you've killed all of the grey areas that create confusion/angst/protests/inadvertent cheats/deliberate cheats.
Alternatively, list each component and the mods/replacement available to it (but this is probably too laborious).
4. Clearly define what is an acceptable replica of a major component.
5. Make it clear whether the lists of acceptable bikes is 'some of the acceptable bikes', 'the ones you don't need to prove' or 'all of the acceptable bikes'. 18.9.0.3 (the equivalent list for sidecars) makes it clear (in that case its 'the ones you don't need to prove').
There's a lot of other small detail things too, but that's the meat of it.
I'm not trying to change the intent of any of the rules - in fact, the opposite is true. I simply want both the intent and boundaries to be clear to everyone with basic comprehension skills, without have to resort to finding and asking people who are 'in the know'.
I stand by all of the above, but have some further thoughts:
I've been reading Classic Dirt Bike, and I am increasingly dismayed by what the pommies do to their bikes, particularly their pre-65 trials bikes, which I feel have totally lost any spirit of their era. Hell, CDB #6 has a short artical on a pre-65 trials bike that 'won't be competitive as a pre-65 bike nowdays, but is representative of what bikes were like in the day'...
No, I'm not suggesting that we should limit bikes to 100% stockers, or even 100% "in the day", but that we have the opportunity to
keep Australian VMX as a good representation of historic bikes that actually do a decent job of resembling what they looked like in the day.