You sound exactly like me, I've spent almost as much as the original purchase price putting this car back to what it should be!
TTE stands for Toyota Team Europe. It's just a styling kit sold as an extra by Lexus, front and back bumpers and boot lip. There's no difference under the bonnet, exactly same engine as every other IS200, unless it has the TTE supercharger fitted which I doubt yours has LOL! Very rare and expensive and were aftermarket.