If the "inspector" does not know the car well, he may not spot
the difference.
Sometimes, they don't even open the bonnet, and if your exhaust
isn't too loud, the car will still pass.
Then again, if you get caught, they will inform LTA who will fine
you for illegal modification, and you have to bring the vehicle
back for 're-inspection' after 're-installing' the original engine.
And you and the car will be "blackmarked".
Best not to get caught. 
I too am seriously considering the SR20DE conversion, but I don't
want to spend 1K each year just swapping the engine back and forth
for just another 30hp. 
I believe that the turbo kit made in the US will get more approval
in time to come, and that will be "semi-legal" in future. For 50hp
increase (with a Garrett T25), it will be a very good upgrade.
With proper mods to the intake, headers, pistons, rods, camshaft,
exhaust system, ECU, fuel system and clutch upgrades, a turbo
GA16DE can get 180-200bhp car at the flywheel.
A suspension and brake upgrade (rear drums to discs, and larger
front discs, slotted and drilled if possible) and the car will be
ready to hit the track.
In 5 years time, if you do see a black Presea at SMSA events or PG
race days, that may just be me 
That's the plan for my baby. 
