In NSW and Vic you can fit a 149 without making any other mods. Anything bigger and you need engineer's report and all the usual other things like discs, 2speed wipers, belts, heater/demister etc etc.
Other states vary, and I'd be interested to know what the rules are in Tasmania. Also, if modifieds are allowed to have some form of limited use rego over there I'd like to know about it - seems NSW is the only place that enforces stockies only on historic/limited use rego.
In other states limited use tends to mean less than 5000 miles/year, typically weekends only. Could you do that many miles on the Apple Isle anyway?
cheers
RET