G'Day all,
I've been lurking around for about a week on this and other forums as I bought a '73 240Z a fortnight ago and am in the learning stage but thought I'd comment on this having just spoken to an engineer a week ago.
Keep in mind I'm in Sydney so my comments may not matc VIC laws but it should be fiarly close if not the same.
NSW is strict on allowed capacity and it's about to become stricter. The old 350 V8 swap hasn't been allowed for a while and under current regs you can go up to a 4.9l capacity. However under the regs about to be introduced that'll be reduced to 4.1. This is for NA, not forced induction BTW and based upon the offical RTA weight of 1041kg for a 240Z. I don't know if these are the long rumoured national guidlines being introduced, it didn't occur to me at the time to ask.
On the subject of aftermarket ECU qik_shift is correct in that if it's a pre '76 vehicle they don't particular care, even with a new engine swapped in. In NSW there's no pollution check, even for the blue slip inspection so you can run aftermarket ECU without any hassles however all original emissions gear must be on the engine and correctly connected.
So there's my quick 2c worth although I will add why bother with the Toyota motor when an RB is an easier swap, I'm sure I saw a mounting kit available for the RB series.
Anyway, love the site, I'm learning lots about Z cars. Now, back to lurking.