I'm almost finished my converion of a CA18DET into a 1200 coupe. in NSW a CA18DET is legal the most you can have is 1825cc's with a turbo'd engine.
The conversion I am sure is legal throughout Aust.

What needs to be changed, well,
engine mounts
a hydrolic clutch installed
New tailshaft
New fuel lines 5/16" minimum, surge tank/swirl pot, pickup pump and main turbo pump, EFI fuel filter
Intercooler installed with piping (optional, but more reliable if you do have one)
modded throttle cable,
If using standard silvia dump pipe it needs to be modded to fit,
custom gearbox mount
Alot of engineers like to see hte Stanza strut upgrade utilised before they pass your conversion
I'll add more when I remember it

Radiator

Cheers
Damo


PS conversion cost is prolly $3500 if your lucky thats a rough figure, depends on if you get good deals on things