3SGTE into late model ST204?, Legal? NSW, AUS RWC? Options

[m4dm4n]

So I've been looking into getting myself my first Celica for some time and love the shape of the ST204/205's. While the 5SFE engine is a monster compared to my current car ('99 Lanos) I still want more. I've spent a fair bit of time reading up on the 3S engines, what power they produce as stock, what they are capable of with a bit of help, and where to get them at rough cost figures.

From what I can tell, they can pretty much be dropped into the ST204 body with a bit of work. I already have a very good condition body lined up ('97 ST204 with ZR trim) that could possibly do with an engine swap (current 5S engine has about 340+ on the clock) though it has been well maintained.

I remember talking with a mate of mine some time ago about this and he suggested it may not be legal (swapping an older engine into a newer body) and I may even have problems getting the RWC for it if it was legal and even then the old wallet would be up for a workout making sure the drive-train wouldn't give up with the extra horses running around under the bonnet.

I've searched around on forums looking for other Aussies that may have attempted this or even completed it for this model (particularly in NSW) however I've found very little, except one that I think was actually an ST205 built for track only.

I'm aware that 3SGTE engines were available between about '94-'99, so if there is such a time-limit on swaps I guess I'd have to be careful to import the right year model...?

Just now I've thought that the 3SGE red-top could also be an option. It would give more grunt than stock and may make it easier to pass inspections/rego etc. I pose the same questions...