I don't know why everyone is going on about older EJs - seriously, with is current emissions hooked up to the older block and heads, no one would know the difference until you got an expert involved.
Vic Roads wouldn't care either IMO.
The EJ22 would be the best option as you wouldn't need to have it engineered. If the EJ25 was an option in that model you wouldn't need an engineer certificate either - but I'd imagine you'd need to upgrade the wiring for that to work properly.
I know the old statement "there's not replacement for displacement"; which I generally agree with, but there are times where other factors come into play - ease of maintenance (and a good track record for being bullet proof), economy, ease of conversion etc.
I must say though after seeing Subaruby's '07 (?) foz at work with the poor low range, it's got some awesome down low torque. He too needs an exhaust to unleash that subi beat
Cheers
Bennie